matplotlib: Update to 3.0.0 (#4434)

Matplotlib is Python 3 only now and has auto backend detection so
move all the backend related dependencies into optdepends.

This splits the package into two PKGBUILD files, one building a Python 2
version providing 2.2.x and one building a Python 3 version providing 3.x+

mingw-w64-python2-matplotlib/setup.py.patch

@@ -0,0 +1,11 @@
+--- matplotlib-2.1.2/setup.py.orig	2018-01-18 07:21:34.000000000 +0300
++++ matplotlib-2.1.2/setup.py	2018-01-25 08:35:39.807755700 +0300
+@@ -102,7 +102,7 @@
+     setupext.BackendGtk3Agg(),
+     setupext.BackendGtk3Cairo(),
+     setupext.BackendGtkAgg(),
+-    setupext.BackendTkAgg(),
++    #setupext.BackendTkAgg(),
+     setupext.BackendWxAgg(),
+     setupext.BackendGtk(),
+     setupext.BackendAgg(),