Add paired t-test greater and less than comparisons

[Magnushhoie]

Add t-test_paired-gt and t-test_paired-ls to StatTest. Currently only the two-sided alternative of paired t-test is available, while e.g. Mann-Whitney provides all three.

Follows the same naming scheme and passes automated tests and manual testing.

[trevismd]

Oh, and perhaps it's worth doing that for independent samples as well, then?

[Magnushhoie]

Hi Trevis,

Sure, tried to add some basic tests for matching p-values. I am struggling to figure out how the TestStatTest tests in tests/test_annotation.py are actually run. I hope the logic will work like it does when I coded it manually.