Add poroelastic outer-rise fault example

[danieldouglas92]

Adds an example that shows a simplified method for using poroelasticity to simulate hydration in extensional faults in the outer-rise of a subduction zone.

[danieldouglas92]

Needs a little more polish still, for example I'm having a hard time generating the images from diagrams.tex so these figures are not working correctly. I also need to add a little more explanation in the step*.md files, but I wanted to get this open sooner than later so what is there can be edited in parallel while I fix up the last few things.

[baagaard-usgs]

I did some minor cleanup all around. See the commits messages and changes for what was needed to bring this in line with the other examples.