pull numerics and physics defaults from their respective modules

[cekees]

@tridelat and @alistairbntl it occurs to me that the default values in default_p and default_n should actually come from the modules they are manipulating. e.g. default_n ought to look like

triangleOptions = MeshTools.defaults.triangleOptions

[adimako]

@tridelat has the recent refactoring with @manuel-quezada fixed this?

[tridelat]

@adimako sort of with #818 (not merged yet), which could be related, but it is not modifying those default_n and default_p files as of now, so I don't think this issue is resolved. (#818 gives each model default and relatively "safe" numerical options (or rather options that should work with most test cases if left untouched). Also, #818 is non intrusive, so the usual way to do things is kept intact.)