Fixed details in antsRegistration interface

The generation of output filenames was incomplete for inverse outputs
in both collapsed and not-collapsed modes.

Additionally, collapsed mode for only-linear registrations was broken
as the warp file was not generated (but checked for existence)
Minor fix ensuring good values in output

invert_flags in collapse mode got unexpected values (not boolean)
for nonlinear transform
set default option
New AddNoise interface

Simple way to add gaussian (signal) and rayleigh (background) noise
to images
Merge branch 'bug/FixAntsInitialization' into experimental
Support all new arguments in dtk interface
Merge branch 'enh/FixDTKTracker' into experimental
nipy.Similarity extended to 4D
Merge branch 'enh/Similarity4D' into experimental
trailing space is probably making travis fail in #798
Merge branch 'enh/AddCSVRow' into experimental
Fixed bug with ants initialization

On one hand, invert_initial_moving_transform was used and needed to
be defined. On the other, as there is a xorg spec with initial_moving_transform_com,
it was still failing.
Merge branch 'bug/FixAntsInitialization' into experimental
PEP8 formatting
Merge branch 'bug/FixAntsInitialization' into experimental
Merge branch 'master' into experimental
Evaluation altorithms separated from misc

Created a new nipype.algorithms.eval group for methods performing
simple error, distance or similitude computations over images.

I think this is better than having them mixed up with, e.g.,
nifti or csv files management.

I also add a new interface: ErrorMap, that computes a distance
function between two images (e.g. two displacement fields). Several
metrics will be available, however now I contribute only with
squared differences maps.
Added masks support in ErrorMap interface
Merge branch 'enh/EvaluationAlgorithms' into experimental
more informative message