Merge pull request #7 from yanikou19/master

First version of Dielectric tensor from Dielectric function
 Add abirun.py
Merge branch 'master' of https://github.com/gmatteo/abipy
 Fix minor problems with plot examples and autodoc
 Fix bug in FileListPanel
 Preliminary version of WorkflowViewer.
 GUI for unit conversion based on pymatgen.core.units
 Add demo for wx converter