Added matplotlib as a dependency for package.
Nosetests! Removed the old structure and added a bunch of new tests.

Previously, all tests were under the test_plotly module. Now, all the
tests are in the nosetests package. Within this, there are separate
test_* modules for different types of fig_to_plotly calls. This helps
keep things separate.

Also, each test module has its own dataset that it draws from. These
sets are kept in the package nosetests/data/.

Currently, there are tests for checking that data goes through, line
plots, and subplots. Bar charts are up next!