Results in lots of churn in the tests, but actually for the better as it
doesn't have to jump through nearly as many hoops to mock things now.

Many providers make their modifications in the order that changes comes. In
python3 this causes things to be inconsistently ordered. That mostly works, but
could result in hidenbugs (e.g. Route53Provider's batching could be completely
different based on the order it sees changes.) Sorting changes consistently
is a good thing and it shouldn't hurt situations where providers are already
doing their own ordering. All-in-all more consistent is better and we have to be
explicit with python 3.

- Added Specific exceptions
- str() instead of concatenation
- removed zone not found warning

Transip sdk also supports a private_key_file,
so forwarding that option to the provider.
Could be handy in combination with k8s secrets.

TransIP allows '@' as value to alias the root record.
'@' was on populate appended with the zone, which trigger an unneeded update.
'@' => '@.example.com.' -> 'example.com'
This fix will stop the unneeded update

- added unit tests for apply functions
- added another json config file for this
- 100% code coverage reached

- added test cases for test_apply, testing for basic create, update, delete records
- added previous state json file in test/fixtures to do the above

- added test cases for testin populate()
- added mock request responses in tests/fixtures/
- updated requirements.txt to require edgegrid-python