fixed systray icon minium height may be 0

Closes #255
_Widget.resize is deprecated

Closes #254
Enhanced Clock widget

* Use self.layout.width to determine if whole bar should be redrawn or not.
* More precise ticks algorithm (it ticks on the begin of the seconds, and
doesn't rely on gobject.timeout_add as it is recommended in its documentation,
see http://www.pygtk.org/docs/pygobject/glib-functions.html#function-glib--timeout-add
for detail)

Closes #185
Import "Running inside Gnome" from wiki

Thanks to @anshumanb for the original content.
Some prompt uses require modified completer results.

This change reinstates the original prompt functionality but provides
the new behaviour via the strict_completer option.

Closes #250
Remove outddated install script

Based on some discussion on IRC, this script is outdated and broken. If anyone
wants to update it, feel free to make a pull request :-)
Remove requirements.txt which went with develop.py
Unify the default widget settings.

Users can now set global defaults for widgets via:

from libqtile.widget.base import _Widget
_Widget.global_defaults = dict(
    font = 'Consolas',
    fontsize = 18,
    padding = 3,
)

in their config, before any widgets are created.

Conflicts:

	libqtile/widget/battery.py
	libqtile/widget/graph.py
	libqtile/widget/systray.py
Remove the need for ugly import hack in config

Now to configure global defaults for widgets, you can just do:

widget_defaults = dict(
    font = 'Consolas',
    fontsize = 18,
    padding = 3,
)

in your config.py

Conflicts:

	libqtile/confreader.py
	libqtile/widget/graph.py
Defaults refactoring for layouts
Update new widgets for defaults system
wip
Fix Zoomy config change.
Set background default value to None.
Remove redundant background default from graph.py.
s/_fontsize/fontsize
Fix more tests/errors due to defaults refactoring
Fix remaining tests

Since the test configs inherit directly from libqtile.confreader.File, we
should not overwrite their attributes with the defaults without first checking
if they exist.
Rearrange some things to avoid circular imports
Remove unused manager imports from widgets.
Notify now needs _TextBox._configure as None fontsize needs to be properly parsed.