add new check for property declaration

Summary:
This check finds property declarations in Objective-C files that do not follow the pattern of property names in Apple's programming guide. The property name should be in the format of Lower Camel Case or with some particular acronyms as prefix.

Example:
@property(nonatomic, assign) int lowerCamelCase;

@property(nonatomic, strong) NSString *URLString;

Test plan:  ninja check-clang-tools

Reviewers: benhamilton, hokein

Reviewed By: hokein

Subscribers: cfe-commits, mgorny

Differential Revision: https://reviews.llvm.org/D39829

llvm-svn: 318117