Tests should be rethought

[parkag]

The idea behind pykCSD tests was to make it compliant with the previous kCSD Matlab library.
To improve the library, there is no point to hold this artificial bound anymore.

The idea is to drop some of the integration tests (?) and add more unit tests.

• the tests should be simple
• the tests should be isolated

Example:
TestKCSD_all_utils should be split into separate classes for each logical part of pykCSD library that they test.