Added Label and Image widgets, as well as some events

Events added include, mouseEnter, mouseExit and mouseMove. Publish
option added to BaseProperty.setTo(), as well as
BaseProperty.hasBeenSet and the anti-recursion mechanisms were re-done
for property subscriptions. Added possibility for property sets to be
ignored by states by default and rounded corners. Borders and the
anchor layout were also added. Also BoolProperty and FloatProperty were
introduced.