lets go icons
Updates start navigation layout

* Adds "Start" text below let's go icon.
* Adds pressed state for "Start" text and icon.
* Updates text sizes, margins, and padding.
* Removes view holder from ItemFragment.
* Uses Butterknife for view injection.
* Adds tests for view components.
Adds line break at the end of lets_go.xml and ic_lets_go.xml
Removes mapzen slogan easter egg.
Uses Butterknife @OnClick annotation for start button listener.
Extracts getRouteRequest() method to improve readability.
Removes view click listener (no longer needed).
Merge pull request #54 from mapzen/start-navigation-text

Updates start navigation layout