added thresholded colorbar

attemps to adress #231

Here is an example for threshold=5 of what it currently looks like:

![bildschirmfoto 2014-11-25 um 18 53 21](https://cloud.githubusercontent.com/assets/3907396/5191981/85c179e6-74f3-11e4-8def-b032366a3684.png)

Greetings from Berlin
good idea!

2014-11-27 11:30 GMT+01:00 Loïc Estève <notifications@github.com>:

> In nilearn/plotting/slicers.py:
>
> > @@ -14,7 +14,8 @@
> >
> >  try:
> >      import pylab as pl
> > -    from matplotlib import transforms
> > +    from matplotlib import transforms, cm as _cm
>
> Agreed but we still have import pylab as pl in a few places. Should
> probably be fixed in a separate PR.
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/nilearn/nilearn/pull/296/files#r20988283>.
>



-- 
Viele Grüße,
Danilo