widget: Refactor W_FORM virtual functions into W_TABFORM and W_CLICKFORM virtual functions.

Instead of a huge if () checking if it's a W_TABFORM or W_CLICKFORM, just split the functions.
widget: Convert getState/setState functions to member functions.
widget: Convert setFlash functions to member functions.
widget: Use QString internally.

Previously, some strings were stored in fixed length static arrays, and others were stored as pointers to the
original (uncopied) data.
widget: Convert getString/setString functions to member functions.
widget: Use delete directly, internally.
widget: Remove unused and useless buttonStartUp().

No, a function which just does "return true;", and is never ever called is generally not considered useful. Not
even as a paperweight. Unless printed on something very heavy, then maybe it could actually function as a
paperweight. However, this commit comment is much longer than the function, so it would make a better paperweight
when printed.
widget: Remove widgStartScreen/widgEndScreen.

They did not seem useful, and widgStartScreen was only called from hci.cpp.
widget: Convert setTip functions to member functions.
widget: Use new directly, internally.

Unduplicated some code.
widget: Remove unused minor tabs from tab forms.

Tab forms had major and minor tabs, but only the major tabs were used, despite a lot of code all over the place for
handling minor tabs.
widget: Partially unduplicate code for various tab orientations.

Left and right tabs are not used, and may or may not actually work before and/or after this patch.
widget: Remove unused psContext parameter in WIDGET::highlightLost() and replace widgRelease() with delete.
widget: Remove unused major tab tips.
widget: Replace WIDGET::psNext with WIDGET::childWidgets/parentWidget, move most clean up to ~WIDGET().
widget: Use new/delete instead of widgCreateScreen/widgReleaseScreen.
widget: Replace bitflag manipulation with WIDGET::show()/hide().
widget: Disable copy constructors/operators for WIDGET and W_SCREEN.
widget: Convert WIDGET::display to virtual function.

Fixes a sign error in tabVertOffset for WFORM_TABBOTTOM.
widget: Keep track of screen pointer, widgets are now safe to delete directly.