Delete useless test classes
Convert 'saveload_test.py' to use with 'pytest' framework
Convert 'PointInfo_test' to use with 'pytest' framework
Convert 'impfn_test' to use with 'pytest' framework
Increase 'PointInfo' test coverage
Convert 'dopri_event_test' to use with 'pytest' framework
pytest: ignore not converted test scripts
Include 'Toolbox/optimizers' tests in testsuite

There are 3 failing tests
Fix evident failures. Mark mysteriously failing test as 'notrun'
Convert 'radau_event_test' to use with 'pytest' framework
Merge identical 'Events' tests for Radau and Dopri in one file
Switch 'TestCommand' in setup.py to 'pytest' version
Proper subclass __del__() implementation

Improper implementation leads to this message in the results of 'python setup.py test' run:

```
Exception AttributeError: "'NoneType' object has no attribute '__del__'" in <bound method InterpolateTable.__del__ of Generator interp> ignored
```
Extend 'clean' command
Merge 'imp_load_test.py' in test for ImplicitFnGen
PEP8
Add config file for Travis CI
Convert 'numeric_diff_test' to use with 'pytest' framework
Implement warnings checks
Add event test for Vode. Change file name accordingly