A collection of various updates

This collects the following changes.
 - Some doxygen-fixes for the tutorials.
 - New methods for the low-level fluid interface SinglePvtInterface.
 - In EclipseGridParser, fix unit conversion error for RS field.
 - Fix an upwinding bug in CompressibleTpfa.
 - Fix robustness issue in SatFuncGwseg* classes.
 - Added gasoilratio() member to BlackoilState, also initialize from RS field of input deck.
 - Added wellRates() member to WellState.
 - More sophisticated WellState::init().
 - In WellsManager, properly initialize control phase distribution factors for surface-rate controls of injectors.