Fixed error in one entry of number_of_triangles table for MarchineCells that results in missing triangles for wedge cell type as reported by issue #496.
It makes me irrationally nervous to check an empty file as the sentinel
data. Instead, add some text that can be compared agains. Also add some
explenation to the file to prevent naive developers from messing with
the file.
Originally, only files in the base directory were put into lfs.
With this change, all files in any subdirectory are also put into
lfs.
Also adding the test files for temporal advection to the data directory.
