Clear bar if widgets don't fill the entire width.

This fixes a bug where a stale widget content can be left in a bar if widgets
shrink to no longer fill the bar width.
Allow more than one STRETCH widget.

All STRETCH widgets get equal width.
Detaching floating windows from the layout implemented
Tests for floating windows fixed
Fixed `wm_type` and added to window info
Fixed `floating = True` in `client_new` hook
Added my config as example of mouse configuration and useful hook for dialog windows
Refactor the way Graph widths are specified.

Users can now specify either a fixed width, or STRETCH to fill available space.
We calculate bar width on the fly, so this is no longer configurable.
Graph housekeeping. meter.py -> graph.py, "bars" init argument becomes "samples".
Add a line graph style.
More graph work.

- Add a linefill graph type.

- Make the bounding rectangle a hard rectangle, rather than a rounded one.
Using a rounded rect, the graph "bleeds out" on the rounded corners, making it
look un-neat. If someone wanted to add the rounded rect back in, I wouldn't
object, but we'd have to do the work to take the corner rounding radius into
account, and fit the graph completely "within" the rectangle.
Get rid of gap at the bottom of linefill graphs.
Revamp the way we specify colour.

In all widget preferences, alpha can now be specified as follows (blue, .5
alpha):

    0000ff.5

    or

    (0, 0, 255, 0.5)

Use this to make graphs look schweet, and move to linefill graphs by default.
Merge remote branch 'tailhook/floatwin' into float
python2 isn't a universal convention, sadly.
Fix various layout issues with graphs.
Initial implementation of global focus order, works only with tile layout
Fixed focus for `Max` and `Stack` layouts
Fixed focus for `Stack` layout in `split` mode
Removed unnecessary calls to `self.focus` in `Tile` layout
Fixed configs in test cases
Newly created windows get focus (this fixes unittests)
Config example with `floating_layout` customization and appropriate focus keybindings