Bunch of stuff (see description)

* Added audio when the player presses the select button (left shift or
joystick 4 [Xbox left trigger]). Plays one of two clips randomly.
* Added a title screen. It does not function yet.
* Updated input settings. No more hard-coding inputs! Now we do that in
Project Settings/Input. Updated several scripts to account for this.
* Renamed the folders, dropping the "RR_" prefix. (If they all have the
same prefix, there's no use for a prefix!) Git Hub shows this as
deleting all those files and folders and adding them back. Weird.
* Fixed a bug with unit costs not displaying correctly.