TEST: fix a test under recent numpys
Removed an unused line in example.
Added resampling to NiftiMapsMasker

Resampling is performed on maps or mask and images, depending on the "target"
parameter, which gives the image whose shape/affine is the reference. Two
targets have been implemented so far: "maps" and "mask".

Tests have been written, they only check for correct shape/affine, not for
the content.
Renamed "smooth" parameters to "fwhm"

Everywhere "smooth" was used as a parameter, is was renamed in "fwhm", to
be consistent with image.smooth().
Add an example using MSDL atlas

plot_msdl_covariance_advanced.py demonstrates usage of an atlas without
the same shape/affine as the data. Two different methods are implemented
(with/without NiftiMapsMasker).