vpy template loading

[Meru]

Currently when you create new vapoursynth script, it starts with these hardcoded lines:

import vapoursynth as vs
core = vs.get_core()

It might be a good idea to load template.vpy instead, that is located in root vapoursynth folder. That script allows user to change contents of the file that is generated by right_click -> new -> new vapoursynth python script, but I think it might be handy for VS Editor too.

[Aleksey Lyashin]

I'm planning a proper snippets system, which would include a new file snippet.