Negations not accounted for when evaluating conditions.

Hello - first of all, thank you for creating this very useful module.

Problem/Motivation

I've noticed that adding a negation to a condition on a message has no effect. I've stepped through the code and where the conditions are evaluated in computeConditionInstance the method doesn't factor in $instance->isNegated()

Proposed resolution

The core ConditionManager evaluation code does the following:

...
      $result = $condition->evaluate();
      return $condition->isNegated() ? !$result : $result;
 ...

In the attached patch I've added that same check and negated conditions now work as expected.

Remaining tasks

- Review patch