Update volume calculations

[finsberg]

The way cavity volumes are calculated are now updated from

$$ -\frac{1}{3} \int_{\partial \Omega} J (\mathbf{X} + \mathbf{u} - \mathbf{b}) \mathbf{F}^{-T} N \mathrm{d}S $$

to

$$ -\frac{1}{3} \int_{\partial \Omega} J (\mathbf{X} + \mathbf{u}) \mathbf{F}^{-T} N \mathrm{d}S $$

where we have removed the base. Reason for this is the base position becomes a bit unstable when base i moving though the simulation.

Also due to ComputationalPhysiology/cardiac-geometriesx#42, the volumes for the LV are now a bit different.