Different simple fixes:
* Getting imports right (mixed up libp3bm.h and libppbm.h)
* Not defining BufSize in every so solver by defining it extern in libbmrm.h
* Correcting wrong initialization of beta[i+1] in libppbm.cpp
* Termination criteria: exit loop if next iteration would exceed CP buffer
Using gtest to run the same tests for all solvers.
* Outsourced dummy data to helper functions create_test_labels() and create_test_features().
Merge pull request #1854 from tklein23/testing_all_bundle_method_solvers

Testing all bundle method solvers (plus cleaning and bugfixes)