Allow gridders to pass kwargs to coord generators

[leouieda]

Gridder methods grid, scatter, and profile now take in **kwargs
and pass them along to the coordinate generation functions. This will
allow extra flexibility for passing in arguments, like a grid height or
configuration, without needing to keep the methods in sync with the
functions.

Removed the coordinate_system mechanics from profile because it
wasn't implemented and is probably gonna take a while. Will introduce it
back when we finally have a geographic coordinate gridder. This
simplifies the coordinate naming schemes and other functions.

This is a step towards #138

Reminders

• Run make format and make check to make sure the code follows the style guide.
• Add tests for new features or tests that would have caught the bug that you're fixing.
• Add new public functions/methods/classes to doc/api/index.rst.
• Write detailed docstrings for all functions/methods.
• If adding new functionality, add an example to the docstring, gallery, and/or tutorials.