Added possibility to filter out LivePreview related log lines

Hey there!

I was missing a possibility to filter out log messages created by the LivePreview window from the ones created by Brackets itself, so I added a button to do just that. When activated it will only show you the log messages that orginate from "your code" and not stuff that is Brackets internal. Hopefully it will make this plugin support another usecase, namely to see what's going on in your live preview window console, since you cannot open the Chrome developer tools to view them yourself without loosing the live preview connection.

I also fixed a small HTML typo and all extra whitespace was stripped away.