[WFLY-1523] Introduce caching for LDAP access by security realms for user searching, caching validated passwords and caching the results of group searches.
[WFLY-1523] Some minor modifications following code review of the LDAP cache implementation.
[WFLY-1848] Enable the loading of the users actual username from LDAP.

This allows a different username to be discovered compared to the one supplied by the user.
Merge pull request #5883 from darranl/WFLY-2848_2

[WFLY-2848] A new option to allow the users username to be re-loaded from LDAP in the management realms.