Require complete description in mesh constructors

[pshriwise]

Based on discussion with @paulromano and @eepeterson:

Currently, the CylindricalMesh and SpericalMesh classes require specification of all grids/parameters upon construction whereas the RegularMesh and RectilinearMesh classes do not. To better follow the tenets of object oriented programming, it would be best to ensure that all mesh objects are valid throughout their entire lifetime. This means updating the RegularMesh and RectilinearMesh classes to require grids (or the lower left, upper right, dims in the case of RegularMesh) upon creation of the object.