LArGeoBarrel code refactoring

Introduced new function LArGeo::buildElStraightSections() which builds GeoStraightAccSection objects and records them into DetStore. This function will be called by the LArDetectorTool when the GeoModel description is built from the SQLite database. The code of this function has been extracted from LArGeoBarrel/BarrelConstruction. As a result of this extraction, for the time being there is large piece of duplicated code, which needs to be resolved later.

A set of auxiliary functions, which are used by the BarrelConstruction class and the buildElStraightSections function, has been collected in a separate place BarrelAuxFunctions(.h,.cxx)