More seamless push

[Paul Chiusano]

typing in manual push destinations is annoying
adding things manually to your config is annoying

what I want:

I type push blah

It remembers that push destination in my config, and associates it with that path (and it gives me a friendly message "I've set blah as the default push destination for this namespace. Now you can push with no arguments if you just want to push there again."). I don't need to manually edit a config file.

If I push with no arguments, it suggests using the default for that path. ("Would you like me to push to the default blah? Either repeat the push command or push.default to push to the default destination without confirmation.")

If there's no default, it checks the parent, recursively, until finding a default or bailing with a nice message ("Sorry, there's no default push destination that I can find. Try help push to view syntax for pushing to different destinations").

If it finds a default in some parent, it pushes to the same relative path. So if I'm in distributed.topics.blah and do a push, it will find a default push location at distributed and then push to <defaultloc>.topics.blah (again with same confirmation step)