WIP: eb_aux_ variables

[skang67]

This PR is a WIP of eb_aux_ variables, which are constructed by combining two eb_cut_cell objects on the low and high sides of a face.

1. We can now access both staggered and non-staggered EB data via the eb_ class. For example:

Array4<EBCellFlag const> const& cflag = (eb.get_const_factory()->getMultiEBCellFlagFab()).const_array(mfi); 

Array4<Real const> const& vfrac =(eb.get_u_const_factory()->getVolFrac()).const_array(mfi);
Array4<Real const> const& afrac_x =(eb.get_u_const_factory()->getAreaFrac()[0])->const_array(mfi);

2. Among staggered eb_aux_ variables, vfrac and afrac have been verified to a reasonable extent.

3. Other eb_aux_ variables are a WIP. I am combining the quantities from two cut cells by weighted averages.