fixed flags for QGraphics(Spot/Center)Item

Signed-off-by: Nicola Ferralis <feranick@hotmail.com>
made size of center settable in config

Signed-off-by: Nicola Ferralis <feranick@hotmail.com>
gui file itself not executable

Signed-off-by: Nicola Ferralis <feranick@hotmail.com>
better uncertainty estimation for initial velocity

Signed-off-by: Nicola Ferralis <feranick@hotmail.com>
changed default parameters for input precision and process noise

Signed-off-by: Nicola Ferralis <feranick@hotmail.com>
also document gui api

Signed-off-by: Nicola Ferralis <feranick@hotmail.com>