[oe] Splitting meta-oe

[Frans Meulenbroeks]

I like the idea of putting toolchains in a layer.

Wrt DP = -1:
I feel if a recipe needs DP = -1 it is not good enough to be added to
meta-oe. Probably it is more something for an unstable layer.
(and DP = -1 encourages the growth of deadwood; I still recall in OE that
there were some recipes that had the last 3 or 4 versions all with DP = -1;
let's try to avoid this in oe-core/meta-oe)

Best regards, Frans.