feat(dx): conditional query by unicode value

depending on whether plone.app.contenttypes is there.
changelog
Feature: Add a new widget : BooleanWidget
We get a checkbox widget to filter contents
which gets a true boolean value for an index (FieldIndex or
BooleanIndex).
Bug fix: fix import of '0' values for boolean properties
which were considered as True when.
Merge pull request #11 from collective/boolean-widget

Boolean widget
Merge pull request #10 from starzel/unicode_index

feat(dx): conditionally query by unicode value
Update Traditional Chinese Message Translation.
[JENKINS] - Fix tests, pylint and pyflakes warnings