First stab at a FeatureService based on scijava-common

Signed-off-by: Ignacio Arganda-Carreras <ignacio.arganda@gmail.com>
Trainable Segmentation: added abstract feature class

This will be the base class for all our features. It includes arbitrary long parameters with String names and double values. The name of the class will be the name of the feature (attribute name in WEKA).
Trainable Segmentation: added Gaussian feature.

For the moment, it works only in 2D, using the GaussianBlue class.
Add a main method to test the FeatureService

To be turned into a JUnit test later...

Signed-off-by: Ignacio Arganda-Carreras <ignacio.arganda@gmail.com>