make paste focuses the pasted cell

This is to make paste behave in the same manner that insert cell above
and below currently work (inserting a new item causes that item to
receive focus).

This solves a problem where, if a user pastes below a cell whose bottom
edge is below the current viewing area, they have no indication that any
action has occurred. The same applies for paste above a cell whose top
edge is occluded.
Add failing test for pretty repr of super() objects
Fix pretty reprs of super objects
Make `SelectionWidget.values` a dict

rename 'labels' and '_value' to 'value_names' and 'value_name'.

To specify a mapping of value names and values, use a dict.
If you specify `values=[list]`, then an OrderedDict will be used.

Assignment after construction only supports a dict.
value_names is read-only
Prevent 'iptest IPython' from trying to run.

Closes gh-4006
don't allow empty selection in selection widgets

raises KeyError on failed lookup (in both directions)
Replace lxml with HTMLParser in citation2latex
Update tests
Crop if no endtag is given
Added 18 more citation tests

Thanks @jakobgager for the tests-
http://nbviewer.ipython.org/gist/jakobgager/6859103
Removed a couple blank lines.
Replace <> with != in citation filter (invalid Py3 syntax)
Import HTMLParser from html.parser for Python 3.x
update selection test with null selection being invalid
pin lessc to 1.4

Not necessarily what we want to do,
but every minor revision of less seems to change how it minifies,
which produces churn.

At least this should prevent accidental churn,
as has recently been committed to master.
Merge pull request #5027 from minrk/pin-less

pin lessc to 1.4
Merge pull request #5025 from jdfreder/jakob-html

citation2latex filter (using HTMLParser)
Merge pull request #5018 from takluyver/i4006

Prevent 'iptest IPython' from trying to run.
Merge pull request #5012 from minrk/selection-dict

Make `SelectionWidget.values` a dict