Add new version `0.5-beta`

git-svn-id: https://plugins.svn.wordpress.org/gitium/trunk@1012111 b8457f37-d9ea-0310-8a92-e5e31aec5664
Update the version to `0.5-beta`

git-svn-id: https://plugins.svn.wordpress.org/gitium/trunk@1012117 b8457f37-d9ea-0310-8a92-e5e31aec5664