Use csv module to create csv strings

[jordanjeremy]

Current csv string creation can produce invalid strings in the event of something like the delimiter being present in a value. Propose using the csv module to create these strings instead of just concatenating values together, to ensure correct strings are created.

Adds argument for csv_dialect to allow user to provide settings for all possible formatting options. If not provided will create dialect based on existing value_separator and line_separator arguments, so they will be used in the event that a user has passed custom values.

[MariusWirtz]

Nice work @jordanjeremy. Thank you.

I will do testing tonight and provide feedback if I find anything.

[MariusWirtz]

There is a small difference between the new implementation and the old one.
The new one includes a linebreak in the last row. The old one didn't.

If it's a small change it would be nice to comply with the old implementation.
Or is there perhaps a good reason to deviate from the old way?

By the way, we have some test cases defined for the CellService class. You can find them here:
https://github.com/cubewise-code/tm1py/blob/master/Tests/CellService_test.py
You can find a small readme on the tests here:
https://github.com/cubewise-code/tm1py/blob/master/Tests/_readme.md

Currently, 7 tests fail due to the two issues I raised above.

[jordanjeremy]

@MariusWirtz that you for the feedback. I will look into the issues identified and follow up.

[MariusWirtz]

The changes look good and all tests pass.

Thanks for the contribution @jordanjeremy!