create top level screens from all controllers listed in a fascs.yaml from the id (pv_prefix) field

Opis for two fastcs services such as these:

fastcs-ioc-01 - single controller
```
index.bob
PV_01.bob
```

fastcs-ioc-02 - multi controller
```
index.bob
PV_02.bob
PV_03.bob
```

Should give us 3 top level screens from {ioc}//{{id}}.bob
```
PV_01
PV_02
PV_03

```

Start by tracing the entry point that reads fascs.yaml and uses the id (pv_prefix) field to generate screens. Verify the single- and multi-controller examples, and consider the work done when one index.bob plus one top-level {ioc}//{{id}}.bob screen is produced for every listed controller.

Written by the indexing model from the issue text.