ImmichProvider implementation

[bugfest]

Fixes #163

This PR implements ImmichProvider as a new network media source. It uses retrofit2 to interact with Immich's API. Only the relevant portions of the API are implemented to keep it simple:

• Basic album information
• Asset Ids and metadata (media type, original file name, location data, description)

This implementation supports password protected and public albums. The connection string is generated in Immich when sharing an album. The user needs to set the album path (containing the album private key) into the provider' settings.

I had to make some minor changes in other parts of the code to allow this provider to work. In particular:

• Included filename field in AerialMedia to allow duplicate removal work when the URL does not end up in a filename.
• Skip metadata matching for elements already containing metadata.

Some screenshots:

[bugfest]

Waiting for 1.7.2 version to come out (new provider integration)