Fix examples on Qt and interactive session.

* Remove explicit wx dependencies.
* Save demo object so that it doesn't get garbage collected in an interactive
  session.
* Minor PEP8 cleanups.
Remove `from __future__ import with_statement`

Also so my cleanups and color tweaks.
More clean ups.

Fix some text, tweak some colors, prevent garbage collection.
Merge pull request #94 from enthought/fix-examples

Fix examples on Qt and interactive session