Allow numerical solve blocks to use values from the sheet

[mgreminger]

Currently, solve cells are isolated from the rest of the sheets and only their outputs can be used in the rest of the sheet. This is fine for symbolic solves since outside values can be brought in through variables. However, for numerical solves, the solve cell needs to be updated if any updates to the systems of equations are needed. This feature would allow a numerical system solve to be defined as a function where some variables are external to the system solve.