Clear session before setup

Fixes https://github.com/owncloud/core/issues/11861
Support HTML in logo claim
fix whitespace
migrate jQuery to bower
still try to encrypt files, even if the session is not initialized. The stream wrapper will throw an error which is better than silently continue.
adjust strings - fixed #11930
ignore core/vendor in scrutinizer
fix typo in content type
throw exception if private key is missing
drop unused jquery.placeholder
Merge pull request #11962 from owncloud/fix-server-sharing-strings

adjust strings - fixed #11930
Merge pull request #11928 from owncloud/support-HTML-in-logo

Support HTML in logo
Merge pull request #11965 from owncloud/fix-jsonresponse

fix typo in content type for JSONResponse
unbold labels and folders
explicitly unbold text by default, otherwise might be bold
Merge pull request #11355 from owncloud/unbold

Unbold
Merge pull request #11968 from owncloud/drop-jquery-placeholder

drop unused jquery.placeholder
Remove confusingly names \OC\User\Manager::delete and fix the automatic cache cleanup instead
Merge pull request #11936 from owncloud/bower-jquery

Bower jquery
bower handlebars