Advanced digitizing tools (aka CAD tools)

This integrates CAD tools in QGIS application.

This is roughly the port of CADinput plugin to core, with some fixes and improvements.

A QEP has been issued: https://github.com/qgis/QGIS-Enhancement-Proposals/pull/8
Thanks for the feedback.
Just a remark, I would like to have another method as evaluateToDouble which has `const QString& text, bool &ok` as parameters since I only have the text from the line edit as input (so no fallback value).
What do you think?