Added updated find_headers.rb from ResearchKit git
Added updated find_headers.rb from ResearchKit git

- Added find_headers.rb from ResearchKit repository.
- Updated find_headers.rb to take a projectfile and a target rather than hard coding them. This makes it easier to use the find_headers.rb in other projects.

tktsubota/CareKit,tktsubota/CareKit,eburns1148/CareKit,eburns1148/CareKit