Feature mesh update controls

Summary

Adds a new update function to dynamicFvMesh that enables users to control how often the mesh is updated for moving mesh cases.

Details of new models (If applicable)

Adds a timeControl object to dynamicFvMesh, i.e. the same controls as used by function objects. This requires the top-level solver to call the new

mesh.controlledUpdate();

function instead of

mesh.update();

Currently applied to pimpleFoam and rhoPimpleFoam only for beta testing, and likely to be rolled out across other solvers in future releases.

Example usage in the dynamicMeshDict

updateControl    timeStep;
updateInterval   5;

Risks

Only applied to the solvers mentioned above (for now) - testing has not shown any regressions.