Make IPAAnsibleModule base class of FreeIPABaseModule.

By making IPAAnsibleModule the base class of FreeIPABaseModule, instead
of AnsibleModule, some methods on FreeIPABaseModule can be removed and
suport for commom parameters in modules using the older class can use
the same commom parameters (ipaadmin_principal and ipaadmin_password)
as the other parameters. This will also allow easier deprecation of
FreeIPABaseModule, which is hard to maintain.

To be able to use IPAAnsibleModule as the base class, it was moved
within the file, to position before FreeIPABaseModule declaration.

This patch also modifies IPAAnsibleModule by:

    * removing usage of `self` in methods not requiring it, turning
      the methods into @statimethod;

    * adding comments to all the methods in IPAAnsibleModule, which
      makes it easier to understand what the individual methods do,
      and what their parameters represent.