add pa-wmenu

[arcxio]

I was just going to add pa-wmenu as wmenu is the default Sway menu, but realized that most of the menu scripts are just copy-pasted and could be abstracted away to a generic script, so that's what I did.

The existing menu scripts are changed to call the new pa-menu and will still work after pulling if they are symlinked to the local pa repo.

[arcxio]

as a bonus, all of the menu scripts are now shellcheck compliant

[biox]

from my perspective, the scripts in contrib/ are meant to be standalone - i'll absolutely accept your shellcheck/pa-wmenu contributions, but abstracting these into a single pa-menu script is too much - lots of folks just copy & paste the thing most relevant to them and the pa-menu abstraction complicates that a little too much for my liking. sorry!!

[arcxio]

that's fair, although I'd still like to suggest utilizing pa list in the existing scripts to make them simpler

[biox]

works for me!