init_log before start importing stuff

This fix stuff trying to log, before Qtile is instantiated
We should look for a better way to make this
add logging on widget imports

now the import errors stop being silent and displays an error when a
widget cannot be imported because it can't meet some dependency
remove timeout_add debug logs, it makes more noise than help
set default logging level to WARNING
add importlib as a dependency for python <= 2.6 and 3.0
fix widgets safe_import on python 3.2
add python 2.6 importlib dependency to the install docs