Fix leaking classes related issue #1477
Revert changes in VwRegressor.cpp
fix a small memleak in SGObject.ref_unref unit test
Fix typo in tests/integration/python_modular/CMakeLists.txt
this should fix issue #1661
reduce number of x-validation repeats and number of parameter combinations in grid-search
decreased number of iterations to make test run faster
Merge pull request #1681 from karlnapf/develop

speed ups for tests
removed notebooks since there will be a more complete one soon