After saving slice fixing redirect

[michellethomas]

When saving a slice and going to a dashboard, the redirect to the dashboard url is breaking. We were redirecting to data.slice.slice_url but data was a string when goto_dashboard is true.

@graceguo-supercat was thinking it may be useful to always return the full slice object, but I can also just return {'dashboard': dash.url} instead of adding it to the response.

Thanks for the help @graceguo-supercat

[coveralls]

Coverage increased (+0.004%) to 70.145% when pulling 5723b14 on michellethomas:mt_fix_save_slice into f8cc05b on apache:master.

[mistercrunch]

Thanks for the fix! Mergin'