Gal mode: graphic cross-air cursor moved on items when clicking on & DRC error, like in legacy mode.
Make popup menu shown when right clicking on a DRC error item working.
* Encapsulate most of the MODULE class.
* Start encapsulating the DIMENSION class.
* Lay some groundwork for EDA_TEXT encapsulation.
* Move cleverly hidden MODULE functions into class_module.cpp.
* Use std::swap to exchange TEXTE_PCB values for undo/redo.
* Remove unused members from MODULE class.
* The usual coding policy and documentation fixes.