Interface to allow Add/Update/Enable/Disable subtypes

Add an interface to allow Add/Update/Enable/Disable subtypes.

Update:
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Freezes basic type and only allows changing the subtype label. Affect should immediately be visible at all the places like contact view screen, create new contact list etc

Disable/Enable:
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Makes a type in-active. Lists displaying types would automatically exclude the inactive type.

Delete:
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Shouldn't be allowed (with a message), if there are any custom data associated with the type being deleted, which is expected to be deleted manually from custom data screen.
Just before the deletion, contact_sub_type value for all contacts (with subtype as type being deleted) should be unset (or updated to NULL)

Disabling Built-in Types - Not Supported for this Release
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NOTE: Much of the work to support disabling of Built-in contact types (e.g. Household or Organization) has been committed under this issue. However, there are still some some open issues / areas to test and handle so we are NOT exposing the ability to disable built-in types to the administrative UI. If you really need that functionality you can experiment with disabling the contact type manually in the DB - ping us on IRC to discuss.