[master] is_strict_content_types

- currently grape is very loose in what call and content_types it allows through it'r params, urls, etc..
- this is an attempt to lock it down (optionally) as well as  fix some redundant code on content_type checking / memory leak checking


I am very open to feedback in whatever way, as I will make the fixes to get this merged. 

please review
I was not sure if there was some existing key like this. Let me know.