Reorganize the version checker project

1) Reorganize the version checker project:
   New Group Id: org.eclipse.cbi.versionchecker
   New Artifact Id: org.eclipse.cbi.versionchecker.ui

2) Make the project more Maven and Tycho friendly

3) Remove VCDBCall class, add VCPostRequest class to enable the
   plugin to consume the web services.

4) Remove MvnP2Util-0.1-SNAPSHOT-jar-with-dependencies.jar

5) Add a mechanism to include two external jar files into lib/
   org.eclipse.jgit
   gson