Fixed JS and CSS issues in users page

- Renamed "delete" to "deleteEntry" to make IE8 happy.
- Added missing "svg" class for the "+" button
- Added height to "+" button but was unable to properly align it

Note: I gave up trying to align the "+" button because IE8 just doesn't want to comply. At least with the new height it is easier to click on.

Please review @blizzz @owncloud/designers 

Without this PR the users page does NOT work in IE8.
Setting to OC 7 CE unless we think that IE8 is not important for that release. (CC @karlitschek @craigpg)