Improvements to the biomineralization exercise for the upcoming course

Improvements to the exercise:

• Change length of simulation to be defined by length of individual processes for biomineralization and CO2 injection: tEnd = InjBioTime + InjCO2Time.
• !138 (merged) Add task for alternative permeability computation using a power law instead of Kozeny-Carman.
• !140 (merged) Discuss implications of simplified precipitation rates in README.md (in conjunction with slides).
• If implementation of SimpleCO2 is merged in time, start the exercise with it and later change to tabulated values as a task?
• Run codespell to fix some common typos