Code cleanup
 Preparing migration to the new test suite.
Merge branch 'master' of https://github.com/gmatteo/abipy
 Start to use the new approach for generating reference files for the test suite.
 New class RunManager to facilitate the different steps of the calculation/test
 Remove kpoints_factory, standardization of k-sampling info in GSR and WFK file is still missing.
 Replace WFK files with GSR files in several automatic tests + use abiopen in examples
 Fixed regression in abipy.gui
 Example for EOS fitting + Gui widget + new version of AbinitInput