* An absent rule is the same as a rule with 'enabled == false', and is not
necessarily 'OFF' (particularly in the case of the bot rule, which is
inverted).
* If we don't understand the rule, then don't tick any of the radio buttons,
and instead show it in the 'external' section.
For notification rules, the absence of a value on a 'highlight' tweak means
that the highlight should happen; this was previously confusing us.
Use the action parser from NotificationUtils to simplify the code.
Fixes https://github.com/vector-im/vector-web/issues/1330
