Revert "Add a parameter to the Grid to allow the default 'walkable' state to be set."

This reverts commit 84d02744378fe766f08ecde1edc2e2fc4170e158.

Conflicts:
	lib/pathfinding-browser.min.js
Revert "Allow the Matrix to be used for non-walkable grids."

This reverts commit 9dc2bd3aabe992a544d330ed9be1a896473cccb0.
fix: test function name
fix: global variable leak
mod: rebuild lib
mod: bump version