Translations:Sketcher helper constraint/5/en

Helper constraints are currently required for:
 * Constraint Tangent (in tangent-via-point mode; two point-on-object constraints are needed)
 * Constraint Perpendicular (in perpendicular-via-point mode; two point-on-object constraints are needed)
 * Constraint Angle (in angle-via-point mode; two point-on-object constraints are needed)
 * Constraint SnellsLaw (coincident constraint and point-on-object constraint are needed)