various and sundry code cleanups and improvements

- We no longer need to create hard link to /usr/bin/osascript named "Lantern"
  in Proxifier constructor to get the title of the authenticate dialog to say
  Lantern, because we no longer cause an authenticate dialog to appear.
  The setuid configureNetworkServices binary is now used instead.
- Remove MacProxyManager. The only method we were using from it was "runScript"
  which is now LanternUtils.runCommand. This is used when setting the system
  proxy on Linux too, so it was confusing to have it in MacProxyManager.
- Increase loglevel to info for Proxifier. The configureNetworkServices call
  may give debug output like:

      cp: /Library/Preferences/SystemConfiguration/preferences.plist.old: Permission denied

  but it's not a problem and we can safely ignore it.
- Remove Proxifier.osxPrefPanesLocked and Proxifier.tryAll. These were for
  checking whether the Network Settings preference pane is locked but the
  setuid configureNetworkServices binary obsoletes them.