Axisymmetric flow

[trevilo]

Add capability to run axisymmetric flow as an option.

[trevilo]

Initial capability for axisymmetric flow without swirl is in 8354b63. Next steps:

• Testing
• Replace #ifdef AXISYM_DEV with input-file-based options and logic (waiting on #88 before starting this)
• Enable swirl
  • Divorce number of velocity components from dim
  • Add azimuthal momentum equation

[trevilo]

• Testing

Two regression tests added:

1. axisymmetric viscous flow in an annulus
2. axisymmetric viscous flow pipe flow

• Replace #ifdef AXISYM_DEV with input-file-based options and logic (waiting on initial refactor of input parsing  #88 before starting this)

Done. Use flow/axisymmetric = True in the updated input file to enable axisymmetric mode.

• Enable swirl

  • Divorce number of velocity components from dim
  • Add azimuthal momentum equation

Done. Could use better testing with swirl though, as both regression tests above are no swirl cases.