RadioMedium: added NeighborCache support.

RadioMedium: display string fixes.
GridNeighborCache: added implementation.

Radio: INeighborCache interface is in RadioChannel.

Radio: CubeNeighborCache implemented addRadio(), removeRadio().

Radio: CubeNeighborCache deleted.

Radio: added an INeighborCache class which implements a grid optimization method.

GridNeighborCache: merged sendToNeighbors() and fillNeighborVector() for efficeiency reasons.

GridNeighborCache: cosmetics.

GridNeighborCache: copyright.

GridNeighborCache: RadioChannel -> RadioMedium

GridNeighborCache: added namespace.
NeighborListCache: added implementation.

NeighborListCache fix: should not add ourselves to our neighborlist.

NeighborListCache: fixed memory leak.
QuadTree: added implementation.

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

QuadTree: added staticNetwork param.
NeighborCaches: merge fixes.

IdealMac & AODVRouting: fixed merge errors.
RadioMedium: sendToNeighbors() gets non-const transmitter.
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.