Inscription REST API

Fixes Partially addresses #126 (closed)

Description

• Adds a redirect from artifacts to latest inscription (when one of the below formats is requested)
• ATF and CDLI-CoNLL output, and a base for CoNLL-U*

* CDLI-CoNLL is in the database, to convert to CoNLL-U we need the Python converter.

Type of PR This PR is a feature.

Technicalities

• Adds a Inscription controller to handle inscription output (HTML output may be removed later)
• Defines custom, unregistered MIME types to describe inscription formats
• Uses a component to recognize inscription formats across the Artifact and Inscription controllers
• Uses separate views for every format to leverage CakePHP's built-in SerializedView
• Goes down the list of acceptable response type to find one that is available for an inscription (not all have CoNLL)
• Returns 406 NOT ACCEPTABLE if no type is fullfillable

Tests

• Run curl -LH 'Accept: text/x-c-atf' http://127.0.0.1:2354/inscriptions/2309985
• Run curl -LH 'Accept: text/x-cdli-conll' http://127.0.0.1:2354/inscriptions/2309985 → HTTP 406
• Run curl -LH 'Accept: text/x-cdli-conll' http://127.0.0.1:2354/inscriptions/2341997
• Redirect does not work yet since is_latest is not filled in the database yet. Change the value to 1 for any artifact (say P000001) and
  run curl -LH 'Accept: text/x-c-atf' http://127.0.0.1:2354/artifacts/1

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.