Add LDAP Authentication and user management

[wujen]

I want to be able to be able to import users and groups from an LDAP server (Active Directory) to provide centralised user management.

[jkowalleck]

@wujen is this similar to #4 ?

[wujen]

Yes, same goal different underlying mechanism.
I am using Dependecy Track with LDAP users and would like to be able to do the same here.