Prevent vim from generating artefacts in .chezmoitemplates folder

[j-xella]

.chezmoitemplates is a quite sensitive folder, because

• chezmoi processes all the files there (note: this could soon improve)
• if there is something wrong with any of the templates, chezmoi may exit. And since .chezmoitemplates folder is checked at the very beginning, this may block most of chezmoi functionality.

I believe it would be better to automatically disable additional files that vim may generate (swaps, backups) when editing files in .chezmoitemplates folder

[alker0]

Thank you for requesting the great feature. It should get to work via #35.