Live update the header menus when managing sites

[nickvergessen]

1. Add on create
2. Modify on update
3. Remove on delete

@juliushaertl interested?

[juliusknorr]

@nickvergessen A quick fix for the app menu is in #19, updating the settings menu as well will require some more changes.

Are external links with quota setting displayed somewhere in the webapp?

[nickvergessen]

Are external links with quota setting displayed somewhere in the webapp?

No,

But I guess main navigation is most important, since it's displayed.