Restore hash

Restore hash functionality in builder. (fixes #169)
Restore visual behaviour  when selecting modules. (fixes #171)

Ok, this went a big pull request.

Basically it:
- redirects `core/5jhj546oh54uhyfld98` to `core/builder/5jhj546oh54uhyfld98` - same for More.
- restores the colour difference between chosen module and dependency
- adds back the hash save/load functionality
- adds some files under `tests/database/` which are usable for testing this and eventually future specs. (Maybe a fallback to those files should be added for when running the site locally/in development) 
- adds a link with the new hash (when the checkbox asking for it is checked)

Thank you @timwienk for help on this

Same as for `core`, we can probably just redirect `/more/:hash`, rather than a regex.