GUI updates, tabs, modals added

This is the shell for the new gui. work still needs to be done
to make functionality dynamic and operational.
Re-structured code

* Divided client and server code into different files
* Renamed files
* Resolved #52
* Resolved #39 - For single sites the password will now be encrypted and
  stored in the database.
Encapsulating common code into classes

Began the work of refactoring ldap and cas objects into classes so they
can be managed atomically. WARNING: This code contains errors.
Completed current refactoring work.

Fixed a variety of bugs and finally got everything running. Here's a
list of the major code & architectural changes to date:

* added _ldapUser_ class.
* moved cas-related code into its own file & renamed to _casManager_.
    * created wrapper functions in _wordpress-cas-client.php_ so we can
      have more control over how _casManager_ is instantiated, etc.
* moved defines into new _cas-client-constants_ file.
Merge pull request #58 from jonathanwindle/issue-4

* Confirmed 6fb53b5 resolves #52 and #39
* Completed regression testing
* Found bug #59: Plugin generates 2 characters of unexpected output
  during activation