Basic testing framework. Example: ./game test pathfinding

Running ./game test <name> will run a test.

Location
Tests are in test/ and under the test:: namespace.

Current tests
Available tests are: sfml, net, pathfinding, and interface_init

How to add a test called <name>:
1) Create the files test/test_<name>.{h,cc},
2) In test.h, include test_<name>.h,
3) In test.cc, add 'else if (which == "<name>")' to
   test::run(string which).
Silence bad valgrind error by defining the seed of WithUuid.
Fix memory leak in batiment.cc: turned pointer into a local member

There was no destructor for the Batiment class. Also, Batiment and Tile
shared a pointer to the same Coordinate object when a Tile was build
using a Batiment.

I didn't find any use for this sharing of data (for instance changing
the coordinates of a Batiment and see the change in Tile) so I turned
the pointers into local members.

Note that Batiment and Tiles now begin with a Coordinate(0,0) object
instead of an uninitialized pointer as their `picture` member.