Add a dependencies check

[hydrostaticcog]

If you run main.py without dependencies installed, a bunch of import errors are raised, and this could be difficult for inexperienced end-users to understand with all of the paths.

Adding a check in main.py, or even classes/mcPy/McPy.py would assist the end user in understanding that they need to run dependencies.py.

Something similar to https://stackoverflow.com/questions/16294819/check-if-my-python-has-all-required-packages/45474387#45474387 could be useful