No need for extra bottom padding in the editor
Don't polute the global namespace
Use `PTL.utils.getHash()` all over the place

We can't blindly rely on `window.location.hash` because Firefox decodes
the value, and we already have a function to deal with that so let's use
it everywhere. This avoids encoding issues in URL hashes.
Simplified building hash params
Added the ability to sort units by submission date

This option is added for the *My submissions* and *My suggestions*
filtering options (as well as the user-specific counterparts), and are
also expanded to the export view.

Fixes #89.
Reduce the number of queries by also selecting related models
Adjust defaults to newer DDT versions