A different way of handling custom Java Scripts

[bouncepaw]

It was pointed out in #258 that the way custom scripts are configured makes little sense.

See https://mycorrhiza.wiki/help/en/config_file#CustomScripts

My idea was to support both internal and external scripts, that's why this URL-based approach made sense. Now, I'm not sure anybody really uses the external scripts, also, it's not a good idea to use them anyway.

I'm thinking of a filesystem-based approach instead. Something like:

wikidir/
   scripts/
      common/
         ...
      view/
         ...
      edit/
         custom-btns.js

Perhaps it should be part of static/, similar to how custom CSS is applied. Also, sounds like a great opportunity to rethink the JS API. I remember some thought being put into the shortcuts so that they could be extended by custom scripts. Nobody does that, probably.