replace any print() + exit() combos with raise

[quantumdot]

Addressing #256, replace any instances of the print() + exit() pattern with an appropriate raise of an error.

[DiegoFernandezC]

Hey @quantumdot, thanks for your contribution.

I think that your changes make sense, but we need to make sure that these changes work well in all cases.

I add a list that includes the cases that I tested. I will edit it to include the future test cases that I will do.

1. Generate a new distance function that returns a None value. I passed it to the Tracker and check this ValueError.
2. Sent a list that did not contain a Detection instance to the update method to test this ValueError.
3. Pass a list of points with the following dimension (2,2,2) to check this ValueError.
4. OpenCV import fail
5. _fail function