Openpnm

This adds the last few weeks of bug fixes and tweaks to the master code. The final release is schedule for July 27th, 2018.

This is a beta release of V2. A more verbose release announcement will come when the beta tag is dropped.

The main addition of this release is a Mixed Invasion Percolation algorithm, which was used in our [recent publication in TiPM](http://doi.org/10.1007/s11242-017-0973-2).

The OpenPNM team has been working VERY hard on V2, which is now available on PyPI in beta form, so this will be the last release of the V1 branch.

Numpy has been warning us for a while that certain indexing tricks would be deprecated, and that moment has arrived. This minor patch fixes a few places in the code where this error occurred.