Return leading image for {{content words="0"}}

Closes #3884
- This PR includes a reimplementation of Downsize@0.0.5 with `words: "0"`. It uses the same parsing methods, therefore guarunteeing identical behavior.
- Tests have been updated to be more extensive.
First pass refactor of GUI readme redux
Implements new Configuration API

closes #3619
- adds new permissions for configuration API
- adds integration tests
- adds configuration API for reading allowed values
Restrict uncapitalise middleware for API

no ref
- Do not lowercase anything after /api/v0.1/<resource>/ to protect :key/:slug
Merge pull request #3898 from halfdan/fix-uncap-api

Restrict uncapitalise middleware for API
Merge pull request #3841 from halfdan/3619-configuration-api

Implements new Configuration API
Fix regex from #3898

refs #3898
Merge pull request #3906 from halfdan/patch-1

Fix regex from #3898
Merge pull request #3903 from JohnONolan/gui-readme

First pass refactor of GUI readme redux
Merge pull request #3888 from felixrieseberg/iss3884-content

Return leading image for {{content words="0"}}