pointreg app-to-gtest (#4205)

* basic app conversion

* add test cases

* split test cases and address PR review

* ThreeImageNetwork already has cube population upstream

* address Fixtures.cpp discrepancy

* move cube reopens to match in merge conflict

* added fixtures

Co-authored-by: Kelvin Rodriguez <kr788@nau.edu>
Co-authored-by: Kelvin <kelvinrr@icloud.com>