Fix help text for platforms and add special cases for default platforms
Working on generalizing platforms, need to worry about backcompat still
Add platforms file to skel
First pass at an upgrader
Merge branch 'devel' into platform-list

Conflicts:
	tools/commands-cordova.js
	tools/tests/cordova-platforms.js
Fix upgrader after running it a few times
Put back a newline
Small fixes
Clean up commands-cordova
Move cordova-platforms to platforms and include server and browser

Summary: We should start pretending that browser and server are platforms just like ios and android. Eventually, we will be able to remove browser, or server, or both even!

Test Plan: I tested the upgrader, and ran some apps with curmeteor. There should maybe be a self-test for this...

Reviewers: slava

Reviewed By: slava

CC: nim

Differential Revision: https://phabricator.meteor.com/D840