Matplotlib is no longer a dependency, updated gitignore.

.gitignore

 *.pyc
+.projectile
+.dir-locals.el
 .cache
+.coverage
 .eggs
-.DS_Store
-.dir-locals.el
-.projectile
 fslpy.egg-info
-.coverage
 htmlcov
 doc/html

requirements.txt

 six>=1.10.0,<2.0
 numpy>=1.11.1,<2.0
-matplotlib>=1.5.1,<=2.0.0
 nibabel>=2.1,<3.0
 indexed_gzip>=0.3.1,<0.4
-wxPython==3.0.2.0
+fsleyes-props>=1.0.0,<2
+fsleyes-widgets>=0.0.1,<1
+wxPython>=3.0.2.0,<=4.0