Allow replays to be opened by just double clicking on the file

[VasilisThePikachu]

This will require that we register a file extension to the operating system. Replays will still be a zip behind the scenes. Server owners may want to mass rename the file extension in their replays archive for the player's best experience.

I will probably do this after #136 as its going to use the same code
Im doing it

This is similar to osu! osz and osk files. They are just zip files but are associated with the osu! game itself. And the game can then unpack the beatmap or skin
https://osu.ppy.sh/wiki/en/Client/File_formats

File extension to be bikeshed... rtreplay for "robust toolbox replay"?

[VasilisThePikachu]

Talked in vc a little about this

We register rtreplay AND rtbundle

[VasilisThePikachu]

Im also making this part off #136