AngularJS 1.1 not working with Rails

Updated default config to add Accept application/json header with the ability to still override that with custom Accept headers.

@tbrooke sent me some info regarding a post on AngularJS regarding the 1.1 release.  It appears that Rails doesn't like when the Accept headers are "'application/json, text/plain, */*".  It used to work because AngularJS also added X-Requested-With set to XMLHttpRequest which Rails seems to interpret and treat as JSON.

I was able to reproduce the errors with AngularJS 1.1 and changing to pass just "Accept: application/json" seems to fix the problem.