Added time_shift() method to Evoked class.

This method extends the functionality of the evoked class by allowing a
time shift of the scale by a certain amount. The data is not touched, but
only the time-axis is changed.
Added unit test for checking time_shift() method in Evoked class.
Additionally, the time_shift() method itself was made more efficient by
unifying the absolute and relative conditions in one statement.
Changed assert_array_almost_equal() to np.allclose() for the data because
it is more robust to variability of scale.
pep8
Merge pull request #539 from dengemann/kill_mutable_defaults

ENH: remove mutables from func params + use handle
WIP/API/ENH: create epochs in ICA space

Here I propose two new convenience methods for the ICA class which
allow useres to directly create epochs in ICA space without previous
export to Raw. This addresses #319
FIX: remove unsuited score func test cases.

Closes #315.
ENH: realizing epochs.sources_as_epochs_from_epochs

+ adding to example
ENH: addressing recent discussion
ENH: ... hwat's new