Sink particle accretion algorithm enhancements and Bondi fixes
Branch name: ticket_452
To-do accretion algorithm edits:
Using kernel boundary values to integrate bondi equations inward within the accretion kernel. Any gas over the prescribed solution will be removed from the kernel and accreted onto the sink particle. This should remove spurious waves being generated off the kernel boundary that propagate into the grid and disrupt the surrounding hydrodynamics.
Force flow within the kernel to be critical or subcritical, this also mitigates spurious upstream wave propagation that previously arose following accretion.
Bondi module edits:
Improved the readability of the Bondi problem module and removed the constraint that the flow be stepped on within the accretion kernel with the bondi solution.
Changed the bondi problem module to be 3D instead of 2D.