switch to user.js over prefs.js

Firefox overwrites prefs.js, making it impossible to update with puppet's notify
pattern. It should never touch user.js, and that file has precedence over
prefs.js, so let's use that instead.
switch to the shorthand argument for indicating which profile to use
manage the user profile with the profile manager

Aurora no longer describes or honors the `-p` flag for specifying a path to a
profile. This patch uses the profile manager to create a new profile iff one
does not already exist. User.js is dropped into that profile and the process supervisor runs it via the profile manager.
add OSX and iterm2 includes, move user.js to the new firefox_profile directory
vendor those new deps and fixup some typos
update the iterm2 package to get around a permissions problem
attempt to override profiles.ini

Firefox's command line switches for starting with a particular profile, specified by path or name, have proven problematic. This patch takes the path of overwriting profiles.ini instead, making the only (and default) profile point at the provided boxen profile.
Merge pull request #2 from mozilla/user-js

100 YEARS FOREVER