Preparing support of turn restrictions (3): Import of turn restrictions

OSM relations of type "restriction" can be imported. According to the restriction type, several entries will be added to the turn cost table. Furthermore, the turn flag encoder is now implemented by the current edge encoders (e.g., foot flag encoder do not store any turn flags) instead of additional turn flag encoders. Import of TurnRestrictions can be enabled by GraphHopper#setEnableTurnRestrictions(true), which is disabled by default and won't be considered by any routing algorithms yet.

The next step will be edge-based routing algorithms which are able to consider those restrictions.