Fix Chrome launch/connect issues on Windows

Fixes several Live Preview launch and connect issues on Windows:

* Trouble relaunching Chrome if a background process like Feedly is installed.
* Intermittent connection issues/timeouts.
* Intermittent issues launching Chrome

This request has two main changes:

1. Use cmd.exe "start chrome" to launch chrome. Previously we were finding the chrome executable and launching it directly.
2. Launch chrome with a custom user profile. This launches a new, clean instance of Chrome that does not interfere with any running instances.

There _is_ one potential drawback with the second change. The Chrome instance launched by Brackets will _not_ have the Chrome Extensions, settings, etc. that the user normally sees when running Chrome. We may want to add a Brackets theme to the custom user profile to make the window easily distinguishable from other Chrome windows.