Make chaco_trait_editor demo qt compatible.
Remove wx.Timer dependency.
Save demo frame instance so that it isn't garbage collected.

Requires https://github.com/enthought/enable/pull/92.

This fixes a segfault which shows up when these examples are run
from a Qt-based IDE.
Fix example so that it runs in existing event loop.

This was a known issue (see FIXME comment that was deleted in this commit).
Remove wx-dependency from data_stream example.

Reuse generic Traits classes instead of requiring a wx app. This change was
thoroughly tested in ipython (with all permutations of wx/qt backends and
ETS_TOOLKITs). This was run in Mac and Windows version of the IDE, and
I checked demo.py with ETS_TOOLKIT set to wx and qt.