Collective.behavior.talcondition

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- Do not break if parameter `expression` passed to
`utils._evaluateExpression` is None.
[gbastien]

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- Added new parameter `error_pattern=WRONG_TAL_CONDITION` to
`utils.evaluateExpressionFor` and underlying `utils._evaluateExpression` to
be able to log a custom message in case an error occurs during
expression evaluation.
[gbastien]

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- Mark elements using behavior with `ITALConditionable` interface so it behaves
like element using the AT extender.
[gbastien]

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- Use CheckBoxWidget for `ITALCondition.roles_bypassing_talcondition` to ease
selection when displaying several elements.
[gbastien]

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- Added parameter `empty_expr_is_true` to utils._evaluateExpression than may be True
or False depending that we want an empty expression to be considered True or False.
Previous behavior is kept in utils.evaluateExpressionFor where an empty expression
is considered True. This avoid managing an empty expression in the caller method
[gbastien]

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- Added method utils._evaluateExpression that receives an expression
to evaluate, it is called by utils.evaluateExpressionFor. This way, this
method may evaluate a TAL expression without getting it from the `tal_condition`
attribute on the context, in case we want to evaluate arbitrary expression
[gbastien]