Patch/osx improvements

This icons are using scale independent PDF template images which make menu item
icon look great on both Yosemite light & dark theme. Also adding new flatter
and higher resolution app icon.

This ensures application is not leaving empty status item.

Importing everything (*) from AppKit takes a while, since we got 3 scripts
doing that, startup could take up to few seconds. This change makes script
import only what they need, improving startup time to fraction of second.

Fix the most blatant issues of the generated .deb

Otherwise the package is only installable on current Ubuntu releases
and neither on future Ubuntu releases (which will use systemd) nor on
Debian and other Debian derivatives (where the administrator can
decided which init system is used).

Fix clone url in README

fix sudo issue in yosemite

Yosemite support

(Slightly modified by apenwarr)

There were still a few conditions under some OSes that would cause
firewall.py to terminate without cleaning up the firewall settings.  'pkill
sshuttle' was one of them.  Ignore a couple more signals to further ensure a
correct cleanup.

(This only affects sshuttle --firewall, which is a subprocess of the main
sshuttle process.  The firewall is supposed to exit automatically whenever
the client exits, and so far that part seems to work reliably.)

For OS X systems without Python 2.5, runpython.c does not compile.
Use python-config to get the paths for the latest version.

This is required so sshuttle can be run from git repository.

The way the Debian package is created is non-standard, and probably
needs redoing anyway.

(apenwarr: also updates to the matching, latest minimal/do)