Add option to disable validation if there is no .jscsrc file

[MoOx]

I work on a lot of different projects. They don't have the same coding convention & I mainly use jscs for personal project so it will be cool to have a way to enable jscs only if there is a reason (a jscsrc file ?)
Is it doable ?

[dmnd]

This is a reasonable idea but I think it belongs as an improvement to linter, not linter-jscs

[moeriki]

This is a highly desired feature indeed.

I switch back and forth between an ES5 and an ES6-Traceur project where I have to disable linter-jscs each time.

[iam4x]

Fixed with ff78305 it will be present in next release.