ostbuild: Rework again, split into components.json and targets.json

The "resolve" builtin now does a lot more heavy lifting; we expand the
manifest.json, and "build" consequently is less intelligent now, more
of a low-level implementation.

gnomeos/3.4/manifest.json

@@ -1,7 +1,7 @@
 {
   "name-prefix": "gnomeos-3.4",
   "architectures": ["i686"],
-  "base-prefix": "bases/yocto/gnomeos-3.4",
+  "base-prefix": "yocto/gnomeos-3.4",
 
   "config-opts": ["--disable-static", "--disable-silent-rules"],