Remote fails if path contains space

Title says it pretty much all.

I'm wondering if there is a reason for not wrapping the paths in `"`s when spawning the `node` process for the server?

It is easy to say not do put space in the path, but once a project is already initialised with many stuff already pointing at a folder it can be quite cumbersome to change folder names.

A fix could be as simple as changing https://github.com/garris/BackstopJS/blob/master/core/command/remote.js#L14 from:
```js
const commandStr = `node ${ssws} ${projectPath} ${MIDDLEWARE_PATH} --config=${config.backstopConfigFileName}`;
```

to
```js
const commandStr = `node "${ssws}" "${projectPath}" "${MIDDLEWARE_PATH}" --config="${config.backstopConfigFileName}"`;
```

Let me know if a PR is welcome?