Fix #1787 Draft.PathArray align

Correct handling of Euler angle calculations.
+ improve error handling in plane fit
+ add new render type to 3d viewer
Unit.cpp/Unit.h: Added get...Dimension() function calls for missing elements of unit signature.
Initial commit for Spreadsheet module (C++ version).
Added PropertyQuantity to the type system.
Fixed spreadsheet import/export functions.
Fixed spreadsheet "open" command.
Added recompute() calls to spreadsheet commands.
Fixed isTouched() methods in Expression class hierarchy.
Implemented FunctionExpression::toString().
Moved Expression classes into Spreadsheet module.
Added FIXME for later.
Spreadsheet: Added support for $ in cell expressions (absolute cell reference).
Fixed error with to many DocumentObservers being created.
Spreadsheet: Added dependencies on other document objects.
Spreadsheet: Refactored code to use CellContent class instead of individual variables.
Spreadsheet: Added insertRows/insertColumns/removeRows/removeColumns.
Added QtColorPicker classes, a part of an earlier Qt Solutions component.
Spreadsheet: Added additional moc file for qtcolorpicker.cpp (internal class generated from cpp file, not header).