implement filter for changes panel

- move toolbar to top of changes panel
- add filters for:
    fulltext, status, branch, owner, reviewer,
    starred changes

Resolves #21
Merge pull request #32 from forrert/features/filterpanel

implement filter for changes panel

- move toolbar to top of changes panel
- add filters for: fulltext, status, branch, owner, reviewer, starred changes

Resolves #21