Enable remote to work with spaces and quotes in path

[BenceSzalai]

Should address #1609, without replacing exec with spawn as #1610 did.

Escaping any argument could be a rather complex thing, but here we only need to handle paths, and that simplifies the solution, because:

• if there is no " in the path we can always just wrap it in "s
• on windows " is not allowed in file names so with this we don't need to think about weird ways of escaping (like ^" or "")
• also, if the path does not contain ' we can wrap it in 's and call it a day
• every other major systems agree on escaping " in shell by \", so if both " and ' is present in the path, we replace occurrences of " with \" and wrap the result in '

Also note that BackstopJS remote so far would simply fail for anyone with either ' or " in their path, just like with spaces, so basically no matter what the wrapPath() function does, it cannot really make things worse for them.

On the other hand I could make wrapPath() return the path without any wrapping if it did not contain a space, that way ensuring exact same behaviour as so far, but with that it'd still be broken for ' and " in the path, so this is a bit more risky, but this way it'll not break with quotation marks in the paths neither.