MH-8100 improved next and previous segment selection; changed some colors (hover, selected, etc.)

git-svn-id: https://opencast.jira.com/svn/MH/branches/MH-8100@14788 e6edf6fb-f266-4316-afb4-e53d95876a76
MH-8100 corrected next/previous segment behaviour

git-svn-id: https://opencast.jira.com/svn/MH/branches/MH-8100@14789 e6edf6fb-f266-4316-afb4-e53d95876a76