Have taken my ten Tusscher 2004 and converted all the units to be consistent
with CMISS units. Everything seems to work ok now.

Things to note:

- Have been using Cm = 0.01 uF/mm^2 in the variable conversions.

- Needed to swap to volume fractions for the d[X]/dt equations and ten Tusscher
gives no indication of the total cell volume, just the cytosolic and SR absolute
volumes. Have gone with volume fractions from the Noble 98 model and they seem
to work, but would be good to get some data to back up/refine these choices.
Couldn't find anything immediately obvious on PubMed.