More specific selectors, javascript cleanup.

* Assigned jQuery selector results to variables for speed.
* Moved all .attr('data') calls to .data() calls.
* Added :data(uid) selector.
* Split the multiselect checkhandlers into separate functions.
* De-duped click event on password change/img.
* Used fluent interface on jQuery object for event binding.
* Removed redundant tag names in class selectors.
* Fixed incorrect date display for last login.
* Added Userlist.has() to search for uid.
* General code convention compliance fixes.

to-do: Group dropdowns currently don't add the admin group after the search result, not sure why yet.
Add the admin group to the group list data.

Fixes the admin group disappearing from the list when updating the display as the result of a search.

This group data should probably be managed on the page entirely by the javascript GroupList object, but this seems like the interim method.
Fix broken span.
Revisions from review.

* Explicit toString()-based getters for uid and displayname data.
* Restored user check for group multiselect in new user creation form.
* Removed jQuery colon expr for uid.
Rebase cleanup.

Removing code that should not have been restored.
Originally removed in 45fd8f6d.
Merge pull request #8473 from owncloud/user-jquery-specific

Make selectors for user management page more specific