restored freetype dependency in matplotlib

This undoes breakage I made in ef53ce529793701b90bb17816fb2733329967f21

Cygwin and Darwin should use host freetype, it should be built by default on Linux
Merge pull request #74 from hashdist/restore_matplotlib_freetype

restored freetype dependency in matplotlib
Add ipywidgets
Add dftatom
dftatom: Fix the rpath issue