allow installation into a virtualenv

 - use sys.prefix instead of hardcoding '/usr'
 - don't try to install the apparmor profile when in a virtualenv
make SHARE point at TBL's share directory

also stop using /usr/local/share/torbrowser-launcher/mirrors.txt as a secondary
mirrors list, and start including one from the config directory instead.
don't use hardcoded path to relaunch self
requirements.txt: add peep hashes and more entries
Merge pull request #122 from leif/virtualenv

allow installation into a virtualenv