Improve quota input field

- Added tooltip with examples
- The quota value returned by the server is now displayed after update
- Fixes #5346
Fixed input field and tipsy positioning in singleselect

If the user scrolls or the window is resized, the formerly cached offset
was wrong. This fix makes sure the offset is re-read before showing the
input field.
fix translation strings
Merge pull request #5638 from owncloud/admin-quotafield

Improve quota input field