multi-definition error if build static libraries

[CanCanZeng]

https://github.com/ethz-asl/maplab/issues/351

like this issue said, the definition of GyroTwoFrameMatcher::getKeypointIteratorsInWindow is in gyro-two-frame-matcher.h file, but it is included by both gyro-two-frame-matcher.cc and feature-tracker-gyro.cc, this may cause multi-definition error if both aslam_cv_matcher module and aslam_cv_tracker module are linked. Would you please move the implementation of GyroTwoFrameMatcher::getKeypointIteratorsInWindow to gyro-two-frame-matcher.cc.