Changed how pheremones work in point

Pheremones are now a dictionary with key=step and value is total number
of pheremones added in that step of the simulation.

Lots of tests are now broken.
Some tests working pheremoneDecay() not

Got some tests working after changing how pheremones were stored.

point.pheremoneDecay() is not working due to dict changing during
popping.
Got point.pheremoneDecay() working

Got it to remove items from list. Clunky but works. Need to implement
oldest first removal.
Old tests passing

Tests that were broken due to changes in point class all seem to pass
now.

Left with purposefully broken tests that need code writing.
Merge pull request #1 from ciaranmooney/point-pheremones

Point pheremones