unit tests for bilbao database.
Merge pull request #18 from yanikou19/master

New logos + small debug
 Remove pbc option from dftscalarfield
Merge branch 'master' of https://github.com/gmatteo/abipy
 Code refactoring
 Refactoring densities and potentials.
 Add databases with the names of the abinit variables.
 Unit tests for AbiInput
 Regenerate Abinit variable database.