Changes required for integration into tickit simulation framework

[thomascobb]

Make sure we use epicscorelibs libca in cothread

Move this as early as we can to avoid loading 2 versions of libca by mistake

Allow AsyncioDispatcher to take existing event loop

Need this if we want to embed IOC in existing asyncio app

Add ability to add arbitrary lines to Db file and test

Need this so we can read arbitrary db file, remove DTYP lines, add pythonSoftIOC records for logic of those records, then have it appear in the db file that is loaded in the IOC
See tests/sim_asyncio_ioc_override.py for an example of this

[codecov]

Codecov Report

Merging #28 (b2cbcff) into master (2878076) will decrease coverage by 0.01%.
The diff coverage is 95.83%.

@@            Coverage Diff             @@
##           master      #28      +/-   ##
==========================================
- Coverage   85.83%   85.81%   -0.02%     
==========================================
  Files          13       13              
  Lines         812      818       +6     
==========================================
+ Hits          697      702       +5     
- Misses        115      116       +1     

Impacted Files	Coverage Δ
softioc/builder.py	95.69% <ø> (ø)
softioc/softioc.py	88.88% <94.11%> (-0.36%)	⬇️
softioc/__init__.py	92.30% <100.00%> (+0.64%)	⬆️
softioc/asyncio_dispatcher.py	100.00% <100.00%> (ø)

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[thomascobb]

@Araneidae Mac builds (apart from python 2.7) seem to be stuck in a queue somewhere on Github Actions, but I think they will work fine, so this is ready for review

[Araneidae]

I realise I have no idea what this patch is doing, certainly no idea what "tickit" is... Not sure I can contribute very much

[thomascobb]

I've commented on the lines I'd like reviewed