N°2996 Remove iTop version from css variables

- $version does not exit anymore in css-variables.css. now its value is computed during setup and equals setup timestamp instead.
    - use precompiled files (declared in datamodels XML files) to check if theme compilation is required or not.
    - referenced images in scss files are included in precompiled file signatures just like scss files md5sum.
    - images declared in scss files with v=$version are reloaded automatically on browser side after each theme compilation (see xxx.png?v=timestamp)
    - precompiled files are replaced if theme compilation occurred. this will avoid same time consuming operation at next setup.
    - code cleanup: arrays / variables renamed

test/application/theme-handler/expected/css/css-variables.scss

@@ -15,7 +15,7 @@
  *
  * You should have received a copy of the GNU Affero General Public License
  */
-$approot-relative: "../../../../../" !default; // relative to env-***/branding/themes/***/main.css
+$approot-relative: "../../../../" !default; // relative to env-***/branding/themes/***/main.css
 
 // Base colors
 $gray-base:              #000 !default;

test/application/theme-handler/expected/themes/basque-red/main.css

@@ -1,6 +1,6 @@
 /*
 === SIGNATURE BEGIN ===
-{"variables":"37c31105548fce44fecca5cb34e455c9","stylesheets":{"css-variables":"1d4b4ae2a6fba3db101f8dd1cecab082","jqueryui":"78cfafc3524dac98e61fc2460918d4e5","main":"52d8a7c5530ceb3a4d777364fa4e1eea"},"imports":[],"images":[]}
+{"variables":"37c31105548fce44fecca5cb34e455c9","stylesheets":{"css-variables":"3c3f5adf98b9dbf893658314436c4b93","jqueryui":"78cfafc3524dac98e61fc2460918d4e5","main":"52d8a7c5530ceb3a4d777364fa4e1eea"},"imports":[],"images":{"css\/ui-lightness\/images\/ui-icons_222222_256x240.png":"3a3c5468f484f07ac4a320d9e22acb8c","css\/ui-lightness\/images\/ui-bg_diagonals-thick_20_666666_40x40.png":"4429d568c67d8dfeb9040273ea0fb8c4","css\/ui-lightness\/images\/ui-icons_E87C1E_256x240.png":"7003dd36cb2aa032c8ec871ce4d4e03d","css\/ui-lightness\/images\/ui-icons_1c94c4_256x240.png":"dbd693dc8e0ef04e90a2f7ac7b390086","css\/ui-lightness\/images\/ui-icons_F26522_256x240.png":"16278ec0c07270be571f4c2e97fcc10c","css\/ui-lightness\/images\/ui-bg_diagonals-thick_18_b81900_40x40.png":"e460a66d4b3e093fc651e62a236267cb","css\/ui-lightness\/images\/ui-icons_ffffff_256x240.png":"41612b0f4a034424f8321c9f824a94da","css\/ui-lightness\/images\/ui-icons_ffd27a_256x240.png":"dda1b6f694b0d196aefc66a1d6d758f6","images\/actions_right.png":"31c8906bd25d27b83a0a2466bf903462","images\/ac-background.gif":"76135f3697b41a15aed787cfd77776c7","images\/green-square.gif":"16ea9a497d72f5e66e4e8ea9ae08024e","images\/tv-item.gif":"719fe2d4566108e73162fb8868d3778c","images\/tv-collapsable.gif":"63a3351ea0d580797c9b8c386aa4f48b","images\/tv-expandable.gif":"a2d1af4128e4a798a7f3390b12a28574","images\/tv-item-last.gif":"2ae7e1d9972ce71e5caa65a086bc5b7e","images\/tv-collapsable-last.gif":"71acaa9d7c2616e9e8b7131a75ca65da","images\/tv-expandable-last.gif":"9d51036b3a8102742709da66789fd0f7","images\/red-header.gif":"c73b8765f0c8c3c183cb6a0c2bb0ec69","images\/green-header.gif":"0e22a09bb8051b2a274b3427ede62e82","images\/orange-header.gif":"ce1f93f0af64431771b4cbd6c99c567b","images\/calendar.png":"ab56e59af3c96ca661821257d376465e","images\/truncated.png":"c6f91108afe8159d417b4dc556cd3b2a","images\/plus.gif":"f00e1e6e1161f48608bb2bbc79b9948c","images\/minus.gif":"6d77c0c0c2f86b6995d1cdf78274eaab","images\/full-screen.png":"b541fadd3f1563856a4b44aeebd9d563","images\/indicator.gif":"03ce3dcc84af110e9da8699a841e5200","images\/delete.png":"93c047549c31a270a037840277cf59d3","images\/bg.gif":"a315146ab814c73632480136576cd271","images\/desc.gif":"0f58b33929095ea17795dd53bbced5d9","images\/info-mini.png":"445c090ed777c5e6a08ac390fa896193","images\/ok.png":"f6973773335fd83d8d2875f9a3c925af","images\/error.png":"1af8a1041016f67669c5fd22dc88c82e","images\/eye-open-555.png":"9940f4e5b1248042c238e1924359fd5e","images\/eye-closed-555.png":"6ad3b0bae791bf61addc9d8ca80a642d","images\/eye-open-fff.png":"b7db2402d4d5c72314c25790a66150d4","images\/eye-closed-fff.png":"f9be7454dbb47b0e0bca3aa370ae7db5","images\/breadcrumb-separator.png":"1e7e50a8f573e230cf1e0f0399c516e8"}}
 === SIGNATURE END ===
 */
 ====CSSCOMPILEDCONTENT====