frontend: custom actions: interface improvements

[ES-Alexander]

Current behaviour

There are three separate tables for available Actions, but each table has quite similar columns, which is confusing, and harder to navigate than necessary.

Expected or desired behaviour

• A combined table for all Actions
  • Should include columns for Name, ID, type, notes (URL / MAVLink Message, etc), buttons (edit, test, export, delete)
  • Should allow sorting by the name or type column
  • Should ideally also allow typing into the name and type column headings to filter
• A combined editor for all Action types
  • Should include tabs or a radio-button at the top, to select the Action type and determine the lower interface elements
  • Should include a name field, with a copyable preview of the resulting ID
  • Should ideally include a list of available data lake variables (and possibly their values, maybe at a 1 Hz update rate), or an auto-complete mechanism for their IDs when typing in double curly braces

Prerequisites

• I have checked to make sure that a similar request has not already been filed or fixed.