Refactor: techui.yaml should be used for components and custom beamline screens

[niamhdougan]

Following design discussion 15/09/26

Desired behaviour:

• engineer creates an icon and provides a PV prefix(1) or component name(2)
• (1) this is checked against techui_support.yaml to see if there's an associated embedded screen e.g. motor jog box
  • if there is, add an embedded screen which has an embedded 'related display' button to the low level PVI screen
  • if not, just open the PVI screen associated with that prefix
• (2) the ixx-service techui.yaml now becomes somewhere you define larger components
  • e.g. DCM which is a combined component screen of multiple embedded motor screens
  • OR anything that doesn't come from an ioc.yaml or fastcs.yaml (can override with custom screens here)

techui-builder creates a registry of all the potential screens based on all an ixx-services ioc.yamls, plus anything in its techui.yaml, then makes all the required screens that are referenced in the synoptic index.bob