Adds functionality to remove a local template.

This enables the UI to remove existing templates from the file system - something that's been requested for some time now.
That's how well I know the code base after one year... The only reason I implemented this was that @warry and discussed it after the team meeting and that it'd be a good thing to have since so many people are asking for it. Never thought it already existed.

My thinking here was there there is some X icon in the UI after the all existing templates. If the user presses the X then there should be a question to verify that he/she really intends to delete the template folder. You're saying that we should have two variants, one that only forgets the template and one that forgets the template _and_ deletes the files if I interpret you correctly?