Add ability to customize XML includes when reloading object

[JonnyWong16]

Description

Add ability to customize XML includes when reloading a PlexObject.

• The default _details_key always has all the includes.
• A partial reload with includes disabled (e.g. reload(checkFiles=False)) will remain as a partial object.
• A full reload() will have all includes so it will be a full object (existing behaviour maintained).

The only potential breaking change is objects that used to have a blank _details_key = '' now have a populated _details_key = key. I don't think this should cause any issues because the _details_key is only used when reloading and it checks for the _details_key or key so it makes no difference if they are now equal.

Fixes#603
Conflicts with #590 (the _includes parameters were refactored)
Requires #606 (isFullObject() needs to check the _details_key instead of key)

TODO: Tests need to be added for reloading with includes disabled.

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated the docstring for new or existing methods
• I have added tests when applicable

[Hellowlol]

Looks good! We only need tests to verify that the behavior is as expected and that we don’t break anything.

[Hellowlol]

Nice. I noticed some tests that failed because of the pr.

[JonnyWong16]

The test needs to be re-run. It looks like my change didn't get pulled into the test.

Line 25:
https://github.com/pkkid/python-plexapi/blob/387ab170723c8a733766cbf72098bc270095a3ad/plexapi/settings.py#L25

But the test says line 24:
https://travis-ci.org/github/pkkid/python-plexapi/jobs/745126871#L886

Edit: Tests pass now. The failing library collection tests are fixed with #606.

[Hellowlol]

Nice work! 👍 the only thing I think we should improve the the doc string of the kwargs. I think we should mention why this can be usefull as we have got questions about speed and reloads before.

I’m gonna leave this open for a day so others have had the time to chip in before I merge

[JonnyWong16]

Refactored the includes to PlexPartialObject so that they are used by Audio, Video, Photoalbum, Photo, Collections, and Playlist.

Doc string for reload() is updated.

[Hellowlol]

Is the include the same for all the classes?

[JonnyWong16]

Most of them are the same when you view them through Plex Web. Some might be extra (e.g. for Playlists) but it doesn't affect the response from the server.