Add more test cases

[icyflame]

A single test case for an IP task is highly confusing, we want the people submitting code for this assignment to think about various cases, and it's imperative that we give them a range of how the graphs might look.

Finally, we should test this code with all the test cases that are in this repository. I think that about 10 graphs with varying colors (essential), densities, font-sizes and bold or normal font, etc should give a good mix of the range of problems that they might face.

[athityakumar]

@icyflame - I've included 10 input images with commit 939bdeb. DO we need more / different types of testing images?

[icyflame]

@athityakumar all graph labels are in black. Different colors is a must to check if the submissions have taken that into account.