Generateds gdscollector

[kba]

Here's the initial work on extending generateDS' GdsCollector to offer more helpful help messages.

This replaces the buildin parse/parseString methods with variants that know about the filename (and passes it on to OcrdGdsCollector.

OcrdGdsCollector should probably have the same interface, i.e. inherit from ValidationReport (which needs to support an alias add_message -> add_error).

Now that the foundations are here, we can discuss what kind of information should be captured and how messages should be formatted.

[codecov-commenter]

Codecov Report

Merging #576 into master will decrease coverage by 1.50%.
The diff coverage is 21.12%.

@@            Coverage Diff             @@
##           master     #576      +/-   ##
==========================================
- Coverage   84.93%   83.43%   -1.51%     
==========================================
  Files          52       54       +2     
  Lines        2941     3012      +71     
  Branches      572      584      +12     
==========================================
+ Hits         2498     2513      +15     
- Misses        332      387      +55     
- Partials      111      112       +1     

Impacted Files	Coverage Δ
ocrd_models/ocrd_page_parse.py	0.00% <0.00%> (ø)
ocrd_models/ocrd_models/generatedscollector.py	68.18% <68.18%> (ø)

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[bertsky]

Now that the foundations are here, we can discuss what kind of information should be captured and how messages should be formatted.

We discussed this briefly in yesterday's tech call: now that we have a ValidationReport along with the PAGE object, which makes validation errors actionable (without the need to repeat validation in dedicated tools/steps), we could add hooks to to_xml for post-processing (e.g. coordinate repair). As a first step, this could be setting negative points to zero automatically.