Automatic box size estimation.

When creating layouts on the fly with `make_eeg_layout` and
`make_grid_layout`, an appropriate box size is now automatically
generated.
Added tests for layout generation
small fixes to comments
Added test for n_col parameter of `make_grid_layout`
doc fixes
!= --> is not
PEP8 fixes
more PEP8 fixes
even more PEP8 fixes. Changes padding parameter of `_box_size`
_box_size now uses scipy.spatial.distance.pdist

SciPy has an optimized function for computing pair-wise distances
between points. Make `_box_size` use it.
pep8 has no more complaints
whitespace around operators
removed unnecessary variable
Fixed input validation of `make_eeg_layout`

I fixed a typo on the input validation and added some unit tests
to check the input validation logic.
Added Marijn van Vliet to whats new page
typo
Moved scipy import up
Merge pull request #1545 from wmvanvliet/marijn-layout-auto-box-size

Automatically compute box sizes