Add new locations type "finite progress"

[etienneandre]

Suggestion by Jaco: add a location type (in addition to "urgent") that allows for progress, but not indefinitely.
For example, a "finite progress" location with a guard x >= 2 would be deadlock-free, while a normal location (without invariant) is assumed to be deadlocked, because we are not forced to take the outgoing transition.
This could be implemented using an extra clock, and global parameter that must be "big enough".