* implement queryFilteredUsingPredicate in FIRQuery;
* add unit test and integration test for queryFilteredUsingPredicate;
* project change of adding the FIRQueryTests.m file;
* refactoring queryFilteredUsingPredicate to split logic into two helpers;
* Replacing FIR_SWIFT_NAME macro with NS_SWIFT_NAME.
This pushes the minimum Xcode version to 7.3, as NS_SWIFT_NAME was
limited before that version (which is why the macro was introduced in
the first place).
* Fixed FIRMessaging header
zxu