Add concatOutput option

Hello @dpup, 

Please review the following commits I made in branch 'es-concat-output-option'.

86395b877581697633aba190c87ea57c7969a249 (2014-01-30 20:13:19 -0800)
Add concatOutput option
Allows generated JS to be concatenated into a single file, which is helpful for using templates on the front end

R=@dpup