How to add filter position to metadata

[eac...@columbia.edu]

Chris came up with a code snippet for tracking filter use in the .yml files and I found it very useful at the most recent beamtime. Here's how to use it:

1. Copy/paste this function definition while in xpdui

2. Give xrun a "filters" kwarg: xrun(0, 0, filters=filter_positions())

This will add a line in your metadata: for example, if only filter 4 is in use, it will add:

filters: {flt1: Out, flt2: Out, flt3: Out, flt4: In}

[Christopher Wright]

https://github.com/xpdAcq/mission-control/issues/81