Add skirt behavior

this behavior is specialzed on avoiding still obstacles (other agents)
and circumvent them.
Allow CrowdDemo to create skirt behavior
Do not avoid obstacles just after target

do not consider obstacles when the final target position is
closer than the obstacle.
Compute exact trajectory instead of using force

compute the exact trajectory allowing to avoid the other agent.
Find segment obstacle based on blocking agent
More resilient method to detect respective sides

between the current agent and the blocking agent, to prevent oscillation
that were occuring with previous algorithm when agent was just passing by
the blocking agent.
Using Detour wrapper instead of system call

- Add missing <cmath> inclusions
Add a sample using the skirt behavior
Using a constant for the maximum number of supported behavior in crowd sample pipelines
Making sure all the navigation behaviors have a virtual destructor
Merge pull request #10 from masagroup/feature/skirt_behavior

Introducing 'Skirt' behavior