Support gcgc vim-commentary binding

[aquova]

Is your feature request related to a problem? Please describe.
Vim-commentary supports the keybinding gcgc which will untoggle an entire block of adjacent commented code. This seems to be one of the few features in vim-commentary not supported here.

Describe the solution you'd like
When the cursor is in the middle of a commented block of code, gcgc will uncomment the entire section, including all the commented lines before and after the cursor.