Vulcanizer: workaround for Windows idiosyncrasies
### Description
As described in Java bug [JDK-4715154](https://bugs.java.com/bugdatabase/view_bug.do?bug_id=4715154), Windows does not allow a mapped file to be deleted, and the mapped memory buffer is only released when the GC decides to invoke `finalize()`, or something like that.

Therefore, in order for `VulcanizingUtility` to have a reasonable chance to delete all intermediate files after vulcanization, it is necessary to force `System.gc()` at the beginning of `clearObsoleteResources()`.

### Expected outcome
`Vulcanize` executes successfully and intermediate files are deleted.

### Actual outcome 
```
java.nio.file.FileSystemException: vulcan\\resources\\filesaver\\FileSaver.min.js: The process cannot access the file because it is being used by another process
```
and intermediate files are not deleted.

### Steps to reproduce
Execute `Vulcanize`.

### Client environment

#### Operating systems
- Windows

diff --git a/platform-web-resources/src/main/java/ua/com/fielden/platform/web/vulcanizer/VulcanizingUtility.java b/platform-web-resources/src/main/java/ua/com/fielden/platform/web/vulcanizer/VulcanizingUtility.java
index 967e3ff664..8ff1cf8339 100644
--- a/platform-web-resources/src/main/java/ua/com/fielden/platform/web/vulcanizer/VulcanizingUtility.java
+++ b/platform-web-resources/src/main/java/ua/com/fielden/platform/web/vulcanizer/VulcanizingUtility.java
@@ -290,6 +290,12 @@ public class VulcanizingUtility {
      * Removes all intermediate files after vulcanisation.
      */
     private static void clearObsoleteResources() {
+        // As described in Java bug JDK-4715154, Windows does not allow a mapped file to be deleted, and the mapped memory buffer is only released when the GC decides to invoke finalize(), or something like that.
+        // Therefore, in order to have a reasonable chance to delete all intermediate files after vulcanization, it is necessary to force System.gc() here.
+        // While this is only significant for Windows, there should be no ill effects on other operating systems.
+        LOGGER.info("\\tForce System.gc()...");
+        System.gc();
+        
         LOGGER.info("\\tClear obsolete files...");
         try {
             deleteDirectory(new File("vulcan"));
['platform-web-resources/src/main/java/ua/com/fielden/platform/web/vulcanizer/VulcanizingUtility.java']