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

Also makes it possible to have "custom" hashes, in case we'd want to do that for some reason. Old website functionality did have that as well, I don't know if any exist.