Blockserver: Create read-PVs for native-only config details

_Part of a greater redesign of Components. See [Configuration and Component Architecture](https://github.com/ISISComputingGroup/ibex_developers_manual/wiki/Configuration-and-Component-Architecture)_

Umbrella-ticket: #2122

When editing a configuration, the format of the data read from the blockserver should mirror the format of the data written to the blockserver, i.e. containing elements (blocks, groups, etc.) native to the configuration, but not any elements imported from components. It should only contain the names of selected components so the full configuration can be reconstructed on the other end.