Rename "Version Control" toolwindow to "VCS"

* "VCS" is shorter thus occupies less space
* "VCS" is more noticeable (3 capitals instead of 2 words)
* "VCS" is clear enough both for experienced and novice users

IDEA-161043

platform/platform-resources-en/src/messages/UIBundle.properties

@@ -54,7 +54,7 @@ tool.window.name.hierarchy=Hierarchy
 tool.window.name.inspection=Inspection Results
 tool.window.name.todo=TODO
 tool.window.name.dependency.viewer=Dependency Viewer
-tool.window.name.version.control=Version Control
+tool.window.name.version.control=VCS
 tool.window.name.module.dependencies=Module Dependencies
 tool.window.name.tasks=Time Tracking
 tool.window.name.database=Database