Issue #94. For GitHub, GoogleDrive, and Dropbox Plugins:
 - Updated README with configuration instructions
 - Each plugin js checks if *-config.json exists. If not it's disabled.
 - Each navbar view, if plugin is disabled will not display in nav menu.
Merge pull request #97 from glennschler/master

 Issue #94. For GitHub, GoogleDrive, and Dropbox Plugins: