QuadTree: added implementation.

QuadTree: improvements, added move() function, comments, etc.

QuadTree: added staticNetwork param.
NeighborListCache fix: should not add ourselves to our neighborlist.
NeighborCaches: merge fixes.
IdealMac & AODVRouting: fixed merge errors.
RadioMedium: added NeighborCache support.
NeighborListCache: fixed memory leak.
RadioMedium: sendToNeighbors() gets non-const transmitter.
RadioMedium: display string fixes.
NeighborCaches: removed scenario-specific default values.
NeighborCaches: added examples.
NeighborListCache: cosmetics.
NeighborListCache: fixed an uninitialized ptr.
QuadTreeNeighborCache: separated the data structure.
util/QuadTree: added implementation.