QtRenderer uses different brushes to fill GraphicalTrack shapes.
Added ColorManager to QtRenderer.
EstimationFilter initialization returns prediction output (predicted state and variance).

KalmanFilter::diagonalVectorToMatrix(vector_t&) method clears matrix for result before operating on it.
Track stores predicted variances.
GraphicalTrack has prediction ellipse based on it's variance.
UPLOAD_TIME and SENSOR_TIME are timestamp with timezone type.

This change is made for covenience in using extract(), which assumes having timestamp with timezone.