refactoring

[felix-salfelder]

pre-qt5 refactoring, untangling, and CI

• [x] fold in tests and extend
• [ ] make all tests pass
• [ ] error handling and error messages
• [x] split SchematicModel, SchematicDoc from Schematic
• [ ] move component code to component implementation
• [x] Prepare QGraphicsView transition
• [x] move parser/netlister out of the way
• [ ] (mouse) actions & undo stack
• [ ] dialogs
• [ ] diagrams
• [ ] wires (interaction magic)
• [ ] zoom/scroll
• [ ] cosmetic stuff

[felix-salfelder]

This has become the first few commits in #898, until "Qt5 related changes, breaks Qt4".

Mostly done except mouse actions and undo stack, which could be easier after the switch to qt5.