The Matrix CS API, and synapse now supports setting the actions for default
rules. Doing that makes managing the rules much simpler from a vector
persepctive since the ON/LOUD/OFF toggle buttons can be implemented by
setting the actions and enabling/disabling the default rules rather than
overidding them.
Overriding the default rules was difficult because it was not possible
to intermingle the evaluation of user-specified rules with the default
rules. So even though you could add a rule with the same conditions as a
default rule, it would evaluate before *all* the other default rules.
Also creating new rules under a im.vector namespace creates challenges
if we want vector to cooperate with other matrix clients that want to
provide a similar set of toggle switches for the push rules.
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