set LOCTYPE and OTHERLOCTYPE as necessary, fix #310

[kba]

This will allow setting @LOCTYPE and @OTHERLOCTYPE.

Default for @LOCTYPE is OTHER and implies @OTHERLOCTYPE = "file" for now.

Setting @LOCTYPE to something different from OTHER will unset @OTHERLOCTYPE.

[codecov-io]

Codecov Report

Merging #328 into master will decrease coverage by 0.4%.
The diff coverage is 82.75%.

@@            Coverage Diff             @@
##           master     #328      +/-   ##
==========================================
- Coverage   91.12%   90.72%   -0.41%     
==========================================
  Files          30       30              
  Lines        1622     1649      +27     
  Branches      313      319       +6     
==========================================
+ Hits         1478     1496      +18     
- Misses        108      112       +4     
- Partials       36       41       +5

Impacted Files	Coverage Δ
..._validators/ocrd_validators/workspace_validator.py	87.39% <100%> (ø)	⬆️
ocrd_models/ocrd_models/ocrd_file.py	90.9% <82.14%> (-9.1%)	⬇️

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