Use git describe in About Dialog

- Replaced Commit Id by Version from GIT_DESCRIBE output
- Injected GIT_DESCRIBE macro at Version.cmake
- Removed timestamping from version description and cleaned its code

Resolve: #460

Signed-off-by: Humberto Rocha <humrochagf@gmail.com>

cmake-proxies/cmake-modules/Version.cmake

@@ -4,7 +4,7 @@
 
 execute_process(
    COMMAND
-      ${GIT} show -s "--format=#define REV_LONG \"%H\"%n#define REV_TIME \"%cd\"%n" --no-notes --no-show-signature
+      ${GIT} show -s "--format=#define REV_LONG \"%H\"%n#define GIT_DESCRIBE \"${GIT_DESCRIBE}\"%n" --no-notes --no-show-signature
    OUTPUT_FILE
       ${_PRVDIR}/RevisionIdent.h.in
    OUTPUT_STRIP_TRAILING_WHITESPACE