Fix folding/unfolding of song information in browse view

This patch deals with issue #26. When clicking a song item in the browse view,
the extended song information of the preiously clicked item is hidden.
Mobile layout changes
Add basic session management
User groups, permissions, adapted rendering, local storage
Add experimental voting system
Merge pull request #28 from cmplex/haggl/issue26

Fix folding/unfolding of song information in browse view
Merge branch 'master' into haggl/database

Conflicts:
	frontend/render.js
	index.html