this is needed because there is no possibility to set $defaultInstance to false after filesystem::init

don't handle public share keys in lib/public/share.php but in apps/files_encryption/lib/util.php instead

use preShare hook only to check if all pub keys are available and the postShare hook to finaly update the shareKeys if the file was shared successfully

NOTE: only encryption work atm

Made sure new user being shared to is added to array of sharing users

Switched it for post_share hook in encryption hooks
Stop a file from being shared if the encryption procedure fails for any users

Added success/fail feedback to personal settings functions
Improved look/layout of personal settings page
Fixed misplaced plain text in ajax scripts