AP_Scripting: Add generator

[WickedShell]

This adds the generator demo from the unconference. It adds a binding generator, suppresses the console prints by default, and fixes the variable shadowing that was breaking compilation.

It also adds a singleton to AP_Notify and promotes play_string to be a public method to let scripts play tones.

[WickedShell]

Removed some extra libraries from the sandbox/default load which saves 24k flash, and runtime ram

[magicrub]

needs rebase

[peterbarker]

Michael and I have discussed the Notify changes.

These allow scripts to play tunes, which is a great feature.

I have reservations about having play_tune on AP_Notify (we don't have a flash_leds interface at the moment, for example - but perhaps we should?). Perhaps it would be better to have a hal.play_tune(const char *str);.

Additionally, with the Notify changes here the handling of the play_tune mavlink message should move out of the backend.

Neither of these are showstoppers and should not hold up merging here.

[WickedShell]

Following the dev call conversation I'm going to go ahead and bring this in now. I've been unable to get synced with Tridge during the week. The conclusion on the call was that it was fine to bring this in as long as it doesn't have an impact while disabled. Given the review on the notify changes from peter I'm going to pull this in now.