#9060: define global unit conversor
#9060: use QGis::fromUnitToUnitFactor in QgsWmsProvider

 in
#9060: use QGis::fromUnitToUnitFactor in QgsDxfExport

 in
#9060: use QGis::fromUnitToUnitFactor in QgsDistanceArea

 in
#9060: use QGis::fromUnitToUnitFactor in QgsComposerScaleBar
#9060: use QGis::fromUnitToUnitFactor in QgsDecorationScaleBar
#9060: use QGis::fromUnitToUnitFactor in QgsGrassGisLib
#9060: Enable degrees as valid DisplayUnit in QgsOptions dialog
Merge pull request #1056 from ahuarte47/Issue_9060_B

[Feature]: Centralize conversion units in one unique function