Publisher: add more abstract methods

[kalisp]

Is your feature request related to a problem? Please describe.
Publisher expects more methods which are not abstract currently in any base class or interface and therefore it is a bit difficult to know that they need to be implemented.

Describe the solution you'd like
At least these methods should be added:

• install
• uninstall
• get_context_data
• update_context_data

And maybe:

• list_instances see comment lower
• remove_instance

These were expected for SubsetManager (for host where is not totally clear which publishable instances are there). SubsetManager is probably obsolete and replaced with Publisher.

[cuID:OP-4339]

[iLLiCiTiT]

Few notes:

• install should not be abstract but should be available with docstring
• uninstall is pointless method that was never used in openpype
• get_context_data and update_context_data is abstract in IPublishHost interface
• list_instances and remove_instance is only for SubsetManager tool which will be removed with new publisher (so it's pointless too)

[BigRoy]

uninstall is pointless method that was never used in openpype

I've actually started using uninstall() in Substance Painter integration since it's installed through a Substance plug-in which the user can disable too. Not sure if that's the way to go in the long run, but just FYI.