New features

• Added locale helpers in terms of keyboard language/layout.
  • archinstall.list_keyboard_languages()
  • archinstall.search_keyboard_layout()
  • archinstall.set_keyboard_language()

These functions work together to help listing, finding and setting a keyboard layout in terminals. Won't work for X-frontends, but will do for CLI installation methods. Added a language selector-helper-function (archinstall.select_language()) with a crude search functionality.

Added all this to the guided template.