[CA-125856], [SCTX-1588]: Fixed the slow AD logon for users with large group memberships, by not caching the names of the AD groups the user belongs to.

- deprecated UserDetails.GroupMembershipNames property and created a function that can be used to get the group names when required.
[CA-125856], [SCTX-1588]: Fixed the slow AD logon for users with large group memberships.
Added some improvements to the UserDetails class:
- kept the UserDetails.GroupMembershipNames property and added a function to get the group names once and then cache them.
- optimized the code for getting user details.
Merge pull request #13 from MihaelaStoica/master

[CA-125856], [SCTX-1588]: Fixed the slow AD logon for users with large roup memberships, by not caching the names of the AD groups the user belongs to.