[syntax_highlight] add context entry "paste as code"
It would be very nice to have a "paste as code" function in the context menu, like the one we've got for "paste as quote". The clipboard's content could than be automatically pasted inside the backticks.
In an extended version, the user could be asked about the code language to use for the paste. (```python...) But afaik this is non-standard and only used by the gajim plugin. So the prio and need for this is pretty low.