add engine signals and tests
Merge branch 'master' of github.com:Neamar/corporate into engine-integrity
Check player has enough money, including other orders
Unique together constraint for game / user
add the m2m player test and signal
Merge pull request #4 from Neamar/engine-integrity

Test engine integrity
Merge branch 'master' of github.com:Neamar/corporate into influence

Conflicts:
	engine/models.py
	engine/signals.py