GScan: search and filter

[oliver-sanders]

Add search and filter functionality to GScan (#139).

• Search:
  • By partial registration name e.g. "foo' matches "fool/bar" and "bar/fool".
  • Accept globs / regex?
• Filter:
  • Filter by "discrete" data only.
  • May involve adding to the GScan subscription to acquire the required data.

A further enhancement would be searching non-discrete metadata via a different interface. E.G. searching by suite title, description or the Cylc7 "group".

Pull requests welcome!

[kinow]

Hm, doesn't look too hard to implement. We have filters already in Tree view, will try to add that to GScan too.