Add option to skip version check

[yebrahim]

It's useful to add a config to skip version checks, especially when running ungit as part of another project, where every new release has to be tested first.

[FredrikNoren]

@yebrahim feel free to submit a PR

[jung-kim]

Can you clarify on what version check are you talking about? are you talking about ungit version check or git version check?

[yebrahim]

@codingtwinky The ungit version, it pops up in the UI when there's a version difference.