Added a new setting to settings.py MAX_MEMBERSHIP_TYPES

- Adding this new settings so that it's easier to change on a per website basis.
Version bump to 5.1.264
Updating the membership module to inherit from the TendenciBaseModel

- Membership types could not be deleted

- Issue #329
Update managers.py

Inheriting TendenciBaseManager on MembershipAppManager model.
Increasing length of pricing label on event registration

- We're doing this because we have a client who has descriptions within their labels.

- The second solution is to create a "description" field that is included with the labels.  Adding a new field adds more complexity to the module that we could potentially avoid.
Removing redundant (immediate check) in membership model

- This check is unnecessary.  The loop operation does not continue if the list evaluates as (python) False.
Returning back MembershipDefault instance on method calls

- In the MembershipDefault.renew method we sometimes create a new membership instance.  Returning back the instance allows us to continue with the active membership record.
Removing extra group refresh statement.

- This is a duplicate call.  The group refresh method is already called within the MembershipDefault.renew and MembershipDefault.join methods.
Version bump to 5.1.265
Merge branch 'master' into bixly-testing