Initial 'Phases' implementation finding SASS variables prefixed $bp-

Basic feature to traverse /css/scss folder structure and find SASS variables prefixed '$bp-', then render as a 'Phases' tab in the menu bar, using remainder of variable name and value for control e.g. $bp-small become SMALL > 24em

Basic support provided for detecting whether px or em value has been specified.

TODO:
- Provide configuration to allow user to set pattern to match variable name on. 
- Possibly order the options based on size rather than order of declaration
- Confirm this works with .sass as well as .scss
- Deal with other browser units of measure