Spotifywebapipython

* Updated `SpotifyClient.PlayerMediaSeek` method to change the `progressMS` check to `<= 0` when invoking relative positioning.

* Updated `SpotifyClient.PlayerMediaSeek` method to add relative positioning capability. This allows you to seek ahead / behind by a specified `relativePositionMS` positioning amount. The `positionMS` argument must be zero to enable this functionality. Note that the relative position functionality is not defined by the Spotify Web API. The functionality was added to this API to support "skip" seeking.

* Updated `SpotifyClient.GetShowFavorites` method to only return podcast show items by default. Prior to this fix, it was returning both audiobook and podcast shows. The new `excludeAudiobooks` argument allows you to return both audiobook and podcast shows (default returned by Spotify Web API).

* Updated `ZeroconfConnect.Connect` method to load authorization credentials for the Spotify Connect `addUser` blob from a `credentials.json` file for devices that utilize librespot / spotifyd. Spotify no longer supports uername / password authentication via librespot (always returns "Bad Credentials" exceptions. This allows the librespot `credentials.json` file to be copied to the spotifywebapiPython storage folder, and used for calls to the librespot `addUser` zeroconf endpoint.
* Updated `SpotifyClient.GetSpotifyConnectDevice` and `PlayerActivateDevices` methods to bypass the call to Spotify Connect Zeroconf Disconnect for devices that utilize librespot / spotifyd. librespot does not implement the Spotify Connect Zeroconf `resetUsers` endpoint, so the request always fails with a 404.

* Updated `SpotifyClient.GetSpotifyConnectDevice` method to force a Spotify Connect Disconnect call to the device if `activateDevice` argument is `True`. The `verifyUserContext` argument is deprecated as well. This was necessary, as Spotify Connect device manufacturers do not use the Spotify Connect Zeroconf Information `ActiveUser` property consistently.
* Added `PlayerTransferPlayback.forceActivateDevice` argument that allows you to force activate the Spotify Connect device as part of the transfer of playback.

* Added `PlayerPlayState.ItemType` property that denotes the type of episode being played: `podcast` or `audiobook`. This property is only loaded when the `SpotifyClient` `GetPlayerNowPlaying` or `GetPlayerPlaybackState` method is called with `additionalTypes='episode'`.