allow dataset argument to take field objects #338

The dataset argument to operations now takes field objects in addition
to request datasets. A number of changes were made to the codebase to handle
this new condition. The includes changing how netCDF files are written.
There is now a method on dimensions to write to an open netCDF dataset objects.
The temporal dimension was also streamlined to include the numeric conversions
that were previously in a netCDF-specific temporal dimension object.
moved to nose attr for testing

Removed dev and longrunning decorators replaced by adding nose
attributes to test. Info on how to run the tests is located in
ocgis/test/base.py.
add method to write user geometries to collection

Added a "write_ugeom" method to "SpatialCollection". The UGID CSV
file was also removed.
added ipython notebook from esgf demo
added support for shapefiles through request dataset

No support for:
 - time variables in a shapefile
 - no documentation yet for shapefile use
moved combinatorial simple tests to test_combinatorial
added "add_parents" keyword argument to AbstractFunction

This keyword argument is set to False by default to not maintain
parent variables following a calculation. For operations, the value
is still set to True to enable iteration to the various output formats.
Merge branch 'next' into i318-icclim

Conflicts:
	src/ocgis/contrib/library_icclim.py
	src/ocgis/test/test_ocgis/test_contrib/test_library_icclim.py