urlselect: add `bind` and `unbind`

- You can use `bind` and `unbind` to configure the external commands.
  Calling it without any parameter will list the available external
  commands.

- Use shorter label for active mode

- Replace "ok" with "copy"
typeass: use utf8 codepoint for multibyte chars

lua \DDD escape sucks. beside, it's easier to lookup characters using
codepoint.