Added initial version of 2D gravity example
Added README.
Delete log files I didn't mean to include.
Removed spatial database files that are created by python script.
Finished setting up gravity example.
Need to have Brad and Matt test it.
Removed obsolete contour meshing example (covered by 3-D subduction).
Improve subduction meshing example. Make Trelis compatible.
Fixed typo.
Updated meshing README.
Small improvements to 2-D gravity example.

Fixed location of inner block. Adjusted solver tolerances (KSP smaller
than SNES).
Updated geometry journal file based on updated surfaces (change in ids).
Merge branch 'baagaard/fix-meshing-examples-trelis' into next

* baagaard/fix-meshing-examples-trelis:
  Updated geometry journal file based on updated surfaces (change in ids).
  Updated meshing README.
  Fixed typo.
  Improve subduction meshing example. Make Trelis compatible.
  Removed obsolete contour meshing example (covered by 3-D subduction).
Merge branch 'williams/add-examples-grav2d' into next

* williams/add-examples-grav2d:
  Small improvements to 2-D gravity example.
  Finished setting up gravity example. Need to have Brad and Matt test it.
  Removed spatial database files that are created by python script.
  Delete log files I didn't mean to include.
  Added README.
  Added initial version of 2D gravity example