WIP: Feature/composite alarm scaling

[aidanrussell]

This implements the composite alarms logic for scaling. It turned out that an explicit "composite alarm" as defined by AWS cannot be used for scaling. However, I was able to achieve the same thing with some hacking - I created a custom alarm consisting of several metrics and then I used a logic where TRUE=1 and FALSE=0 since AWS alarms require a continuous scale - you cannot explicitly use a boolean scale. Note that we may be exiting AWS recommended formats in the sense that I've had to hack this to some extent, there may be good reasons they are discouraging boolean settings for alarms - but to my mind it's sensible so let's see how it responds to typical user behaviour.