Support for templates to fork

[gokatz]

In most of the cases, I'm creating twiddles for small POC or bug reports. Most of such twiddles will be having simple functionalties that will be repeated over (say, a simple route other than application and a button wired to an action). Ability to mark a twiddle as a template will be extremely handy. So, that we can fork directly from the home (gist) page. As of now, I'm doing this by copying an existing twiddle after going into the twiddle from "My Saved Twiddles". Since we are using github gist to store, I'm not sure if this is possible, as of now.