Add navigation bar (including different changes to make it work).

- Include UI Bootstrap (Bootstrap components in AngularJS).
- Move use of sessionStorage to sessionService.
- Include jwt-decode to read the content of token (for now: username).
- Misc. fixes/changes regarding expired JWT token, layout, ...
Navigation bar: add divider above "Sign out".
Add footer (bottom line) + make signin panel relative again.
Merge branch 'layout-navbar-footer'