Changes in Algorithm documentation
fixed Visualization init file
Merge branch 'master' of https://github.com/PMEAL/OpenPNM
Documentation updates
Merge branch 'develop'

Conflicts:
	OpenPNM/Algorithms/__LinearSolver__.py
	OpenPNM/Visualization/__init__.py
	docs/userguide/algorithms.rst
re-adding diffusivity file that was lost during merging
This file has been sitting in the main dir for ages with no purpose!  Gone.
Added a filter_indices method
- The method takes  list of pore or throat indices, and returns a list of indices filtered by the labels and logic specified
- Also updated the list_pore/thorat_prop/info methods to return an alphabetically sorted list.
Removed filter_indices and extended the functionality of  has_labels instead
- has_labels now returns a boolean mask or list of indices
- Added the option to re-seed the random number generator to pore_seed and thorat_seed
- Removed the try/accept logic from GenericGeometry since get_pore_info now accepts any type of info (passed in through the locations argument)
Fixed bug in OP
- The invasion points were being calculated as a range between the max and min throat capillary pressures, however, due to numerical error sometimes the end points were actually less than (or more than) the capillary pressures.