Made sure main content id isn't required.

Conflicts:
	h5p.classes.php
Made it possible to delete libraries without having to load them again.
Merge branch 'master' of github.com:h5p/h5p-php-library

Conflicts:
	h5p.classes.php
Fixed so that filtered params can be stored in the contents table.
Made it possible to display the library list in a human readable form.