Test that three valent nitrogen cations (radical) are not allow to be aromatic [bug:1332]

Signed-off-by: Egon Willighagen <egonw@users.sourceforge.net>
Check for normal valence in aromatic model before anything else.

Signed-off-by: Egon Willighagen <egonw@users.sourceforge.net>
Allow five valent nitrogen for non-charge separated representation, see pyridinone test case.

Signed-off-by: Egon Willighagen <egonw@users.sourceforge.net>