lab: name the base image's age, refuse a stale one, and rebuild it (issue 698)

A bed machine carries the package database its base image was built with,
and the mirrors stop serving it within weeks: genesis-keeps-its-bus failed
on a 404 from an image 44 days old, with nothing saying its age and no mesh
tool to rebuild it. lab_check and lab_run now say the age, lab_run refuses
an image older than 14 days and names the remedy, and lab_base reads the
image and rebuilds it with mesh-lab's base build when asked.

modules/lab/tsconfig.json

@@ -8,5 +8,5 @@
     "skipLibCheck": true,
     "noEmit": true
   },
-  "include": ["tools/index.ts", "tools/runs.ts"]
+  "include": ["tools/index.ts", "tools/runs.ts", "tools/base.ts"]
 }