Fixed bug in randomFloat.

On 64-bit machines randomFloat was always returning very small
numbers since it was using std::numeric_limits<long int>::max()
as the maximum value. Changed this to use RAND_MAX.
Merge branch 'master' of github.com:jbromley/ColorBoxes
Fixed crash when canceling drawing an edge.

The create edge code was still running on mouse up after canceling an
edge. Fixed to only run if there is still an active edge.
Added more convenience color accessors.

Added accessors for green, blue, yellow, magenta, and cyan.
Changed colors of edges. Use convenience color accessors.

Changed the edges to by cyan while drawn and light magenta when
finalized. Changed the Wall class to use the magenta color constant.
Added name of Linux executable to .gitignore.