Conda recipe and Xarray IO wrappers

[PeterDSteinberg]

Replaces #2 - (I pulled the latest from #1 into the #2 branch and then pushed to ContinuumIO fork instead of @gbrener 's ).

Status: I can build a package with:

cd whitebox_tools/
conda build -c conda-forge conda.recipe --python 3.5
conda create --name wb-test -c ioam -c conda-forge --use-local holoviews pandas bokeh jupyter pytest whitebox_tools python=3.5
source activate wb-test
cd ../../  # To where you EarthSim cloned
jupyter notebook

But a few problems still need to be fixed in #1 (that were evident when importing from whitebox_tools.whitebox_tools.tests.