Remove unused imports
hds: remove swf argument (it was unused)
service.sr: use if "foo" in dict instead of catching KeyError
utils: Remove unused arguments for get_http_data()
Remove unused variable warnings
hls: catch KeyError exception by name
Make all services inherit svtplay_dl.service.Service
utils: import socket
Isolate py3/2.7 conditional imports to own modules
Restructure makefiles

This change makes it easier to add new packages; it's only necessary
to update the sub makefile (lib/Makefile) and add new packaes to the
PACKAGES variable.
Merge pull request #41 from olof/pylint-fixes

Pylint fixes