Get more metadata from ocrd-tool.json

[mikegerber]

There's the potential to get more metadata from ocrd-tool.json than just the version.

• project URLs (Homepage and Repository)
• description

This needs more investigation, as, for example, there seems to be no project level description in ocrd-tool.json (they are per tool) and we would need to check the OCR-D specs for the URLs.

[mikegerber]

• The project URLs can't be dynamic if I read the setuptools docs correctly
• There is no project level description in ocrd-tool.json

And:

• These fields are not as important to keep in sync as the "ever-changing version"