We need a global view of face-area fractions if aquifer connections
happen to be shared between processes. Add a new helper function,
BlackoilAquiferModel::computeConnectionAreaFraction()
that performs a collective operation to compute the total face areas
and then defers to the local aquifer objects to compute their face
area fractions.
While here, also split the initialisation of analytic aquifers into
two parts, one for the face area and connection mappings, and one
for the connection depths. Run the former as part of the object
constructor and the latter as part of 'initQuantities()'. This
ensures that we can computeConnectionAreaFraction() for all analytic
aquifers before assigning solution quantities from the restart file.
