Move all pytest fixtures to conftest.py file

[dorothykiz1]

closes #1030

[datapythonista]

Any reason why moving everything at once, when we discussed about moving one fixture at a time (or smaller chunks of few fixtures if that makes sense)? CI is red, as the last time you tried this, and I guess you'll again have a hard time to find out what the problems are with such massive PR.

[dorothykiz1]

Thanks @datapythonista let me do this

[dorothykiz1]

To be revised