CoNLL-U and CoNLL-RDF export

Fixes Partially addresses #126 (closed) Partially addresses #242 (closed)

Description Cleans up some of the view traits used for exporting, and implements views for CoNLL-U and CoNLL-RDF.

Type of PR This PR is a feature.

Technicalities

• adds CoNLL-U and CoNLL-RDF converters to the Node.JS service
  • Note: not optimal, as Node.JS has to communicate through the CLI. However, the servers could easily be replaced by Python and Java servers respectively, in this container or another, without having to change the PHP end of things.
• adds a CLI for CoNLL-U that supports stdin/stdout
• adds caching for CoNLL-U and CoNLL-RDF conversions (!)

Tests

• Run curl -LH 'Accept: text/x-conll-u' http://127.0.0.1:2354/inscriptions/2341997
• Run curl -LH 'Accept: text/x-conll+turtle' http://127.0.0.1:2354/inscriptions/2341997

Checklist:

• My pull request has a descriptive title (not a vague title like "Update index.md").
• My pull request targets the phoenix/develop branch of the repository.
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• I added tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no visible errors.