Add hasShuffle and hasLoopStatus properties

[llewelld]

Adds canShuffle and canLoop properties to indicate whether or not the Shuffle and LoopStatus properties are supported.

These work by exposing/hiding the DBus property, so work within the MPRIS specification.

[llewelld]

I was in two minds about the naming. Maybe canControlShuffle and canControlLoopStatus are better than canShuffle and canLoop?

[Tomin1]

I was in two minds about the naming. Maybe canControlShuffle and canControlLoopStatus are better than canShuffle and canLoop?

I think they could be better names for this.

[abranson]

I'm not sure. canControl would imply that those properties are set to something that's read only if it's false, while the implementation presents them more as null. I'd say 'hasShuffle' is more accurate than 'canControlShuffle', but 'canShuffle' is closer and more consistent with the other methods.

[Tomin1]

I agree with Andrew's comments about the naming. That hasShuffle() should be considered as an alternative. I suppose mpris specification won't get any canShuffle() method, but if it did, these might collide a bit.

[Tomin1]

I changed these to my liking but of course someone else should review the changes. I can also squash them if the new changes are fine.

[Tomin1]

I'm not sure. canControl would imply that those properties are set to something that's read only if it's false, while the implementation presents them more as null. I'd say 'hasShuffle' is more accurate than 'canControlShuffle', but 'canShuffle' is closer and more consistent with the other methods.

I noticed that there is also HasTrackList property in the specification, so these 'has' prefixed names are not that alien to mpris after all. In some ways that is a bit analogous to 'hasShuffle' and 'hasLoopStatus' as it's exactly that whether something is exposed through D-Bus or not ('HasTrackList' determines whether there is a track list API or not).

I wasn't yet sure which we should prefer so I didn't change the naming. I need to consider it myself still but I might change it still.

[Tomin1]

I updated the naming and adjusted the docstrings a little more still. I didn't touch introspection but I think that while it would be good to do it properly, we could also leave to another PR, if we want to get this merged sooner.