solver: Registered to database

This change lets the solver be looked up from the region database, so
that aspects of the solution algorithm can be accessed by
functionObjects and fvModels and similar. For example, a fluid solver
could be looked up as follows:

    const solvers::fluid& s =
        mesh().lookupObject<solvers::fluid>(solver::typeName);

applications/solvers/modules/compressibleMultiphaseVoF/compressibleMultiphaseVoF.C

@@ -100,7 +100,7 @@ Foam::solvers::compressibleMultiphaseVoF::compressibleMultiphaseVoF
     momentumTransport(momentumTransport_())
 {
     // Read the controls
-    read();
+    readControls();
 
     if (correctPhi)
     {