bug(linux): Install all keyboards in a package

Currently on Linux we install only the first keyboard in a package. This should be changed to install all keyboards included in the package (e.g. [galaxie_greek_hebrew_positional](https://keyman.com/keyboards/galaxie_greek_hebrew_positional)).

We need to think about what should happen if the user specifies a bcp47 code on the command line when installing that keyboard. Probably only install that language if it's included in the keyboard, otherwise install the first language in the keyboard. This means specifying arbitrary languages wouldn't be possible for multi-keyboard packages.