Feature/copy tickets

This PR updates the way we save the time_available property on the base user model. In addition, there are some other translation fixes. 

The time_available property was unnecessarily complex with its own model. However, we needed that property translated and that was not possible with our current api. Instead, a key is now saved via a CharField and Javascript translates the key.

In doing so, I changed the property from time_available to available_time to prevent issues with migrations (same name issues). 

There is a corresponding PR in the 1% repository with 2 schemamigrations and a data migration. At some point we'll need to apply similar migrations for Booking.