Use displayName in the From field of outbound email about new shares.

This is important in the Active Directory case where users are
currently getting a GUID in the From field, making emails look quite a
lot like spam.
Users: use DisplayName in the Display Name col when appending users
Merge pull request #2598 from ceri/master

Use displayName in the From field of outbound email about new shares.
Files External: show display names instead of internal user names in Settings UI
Fix lost ETag on Cache Upgrade
Performance: prepare queries only once
Upgrade FileCache on ownCloud upgrade for all users with files
Remove Debug output
Change LIMIT in DB query respectively remove where not necessary
Port OC_Property Table Index
Port Icewind's fix I
Cache: fix property path for getting legacy etag
Adjust to Icewind's fix
Add PHPDoc
Only prepare an SQL statement once.
Cache: Do not overwrite ETag when file did not change
Cache: on equal mtime also for equal size before keeping ETag, at least makes Unit Test happy
Share Dialog: show Displayname instead of internal name
Whitespaces
[tx-robot] updated from transifex