Implement local file selector dialog

Wrote promise versions of data 'getters'.
Refactored init code to use promises, allowing for easy async handling.
Added JQuery-UI dialog to select local files.

TODO:
  - check if files selected if local selected (otherwise will hang)
  - style dialog
  - check that desc parsing code suitably replaces upstream code
  - investigate reload with new data without refresh
Alter handle_input to consistently use JQuery, not vanilla JS