Restuctured hierarchy of cpp and test files.

In order to make space for POMDP source files and tests, the source
files now mirror the structure found in the include/ folder. In addition
tests are now divided by type (MDP, POMDP, etc). This also allows for
users to compile for example only the MDP library, without the POMDP
library (since this last one will probably have more requirements, such
as lp_solve).
In addition an invalid access bug in WolfPolicy has been fixed.