Merge pull request #554 from zzottel/master

update to German translations
doc updates
rev update
a couple of "not quite public" fixes
Merge https://github.com/friendica/red into pending_merge
Some more buttons. Not ready yet. Changed in private message -submit- to -send-. Confusing in other language(s).
booboo
Merge https://github.com/friendica/red into pending_merge
prevent obscured email notifications
implement max_import_size
remember activity setting
allow channel login to the api, just like with the cloud
make mention tagging by webbie do the right thing.