Base setup for column setting component population

- Adding "columnsService" factory which will be responsible for querying google visualization api to obtain and return configured spreadsheet worksheet columns data
- spreadsheet settings controller now watching for changes to sheet property of additionalParams.spreadsheet object so logic can be put in place for updating/refreshing column setting component
- settings HTML now importing google jsapi and loading the visualization api
- spreadsheet settings app now adding dependency on visualization module from widget-settings-ui-core
Merge pull request #19 from stulees/master

Base setup for column setting component population