Implemented new, simple system boot config and sane default value system

This patch (untested) allows to simply select a pre-configured airframe using a single integer (param SYS_AUTOSTART) and the system will boot what developers consider best for this platform. This will *greatly* simplify user setup and serve well for the majority of users.

It will also limit the bit rot on microSD based startup scripts.

Setting SYS_AUTOCONFIG to 1 tells each platform script to re-load the platform defaults (e.g. controller gains) and will further help users to get viable default parameters for the airframe they loaded.

Since it means that only two parameters need to be operated from within the GCS to configure a platform from scratch, it will also simplify GUI based setup a lot and allow us to offer this quite soon.