UNSTABLE. Do not merge with this commit\!
Merge remote branch 'origin/niek_vanalles' into pieterb_conext
UNSTABLE. added beehub_resource.php
First code to allow changing group/sponsor membership through properties
UNSTABLE, refactoring inheritance tree.
merged with niek_vanalles
Sponsor membership should now be managed through a POST request

* property DAV: group_member_set can be used for setting (accepted) members, but
* to add a membership request you need a POST request
* to promote or demote users to admin, you need a POST request

Privileges aren't checked yet!
Merge remote branch 'origin/pieterb_conext' into niek_vanalles
UNSTABLE. tijdelijke commit met aanpassingen van niek en pieterb.
UNTESTED: made it possible to change group memberships through a POST request on the group
UNSTABLE. but at least testable
Merge remote branch 'origin/pieterb_conext' into niek_vanalles

Conflicts:
	src/beehub_group.php
	src/beehub_sponsor.php
	views/sponsor.php
Beta. Getting more stable by the second
UNSTABLE: Fixed the sponsor part largely
Merge remote branch 'origin/pieterb_conext' into niek_vanalles

Conflicts:
	src/beehub_group.php
	src/beehub_sponsor.php
Sponsors and groups pages tested and fixed