nlu run should work without .nlu.json file in CWD

[ORESoftware]

if we have:

root/
   foo/ 
   bar/
   baz/

if we run nlu run in the root dir, it should search for .nlu.json files in all dirs, with depth 3 by default.

[ORESoftware]

for now it's

nlu run --umbrella --all

but that should be collapsed into one flag, the all flag is probably unnecessary