bashlib and XSD issues

[kba]

• Make input-file-grp and output-file-grp mandatory
• Re-introduce ocrd__raise
• Add a function ocrd__minversion that will check whether ocrd --version is new enough for the processor.
• Move XSD into root package of ocrd_validators

[codecov-commenter]

Codecov Report

Merging #512 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #512   +/-   ##
=======================================
  Coverage   79.70%   79.70%           
=======================================
  Files          45       45           
  Lines        2739     2739           
  Branches      539      539           
=======================================
  Hits         2183     2183           
  Misses        448      448           
  Partials      108      108           

Impacted Files	Coverage Δ
ocrd_validators/ocrd_validators/constants.py	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update cd7be4e...c47e074. Read the comment docs.