core: Root and Frontend maven poms cleanup

- Moved gwt plugin repo from frontend module into root pom
- Description changes to modules description tag
- Organized project properties into sections with comments.

Change-Id: I4fb4647e0d704fc6c2bece9b1b7ea42ea53fac15
Signed-off-by: Asaf Shakarchi <asaf@redhat.com>