Force retrieving a spreadsheet based on previously saved data

- Adding 'fileId' to the "spreadsheet" object on the scope to save and use for providing to the sheets service for retrieving the spreadsheet worksheets data
- Ensuring "docName" and "docURL" are now on the spreadsheet object of the scope to be able to populate the template based on previously saved spreadsheet file
- Using a local "getSheets" function for reuse and watching the "fileId" value for a change so to call that getSheets function to accomodate the situation that a spreadsheet has previously been saved
- Updating template to reference "docName" and "docURL" from the "spreadsheet" object on the scope
Merge pull request #20 from stulees/chore/force-getsheets

Force retrieving a spreadsheet based on previously saved data