User oriented feature support.

[tinevez]

This PR adds feature value storage and facilities to compute them for the MaMuT model.

Feature storage.

• General feature model stuff is in package org.mastodon.revised.model.feature.
• The MaMuT Model has now a FeatureModel.

Feature calculation.

• For MaMuT, API consumers can extend special interfaces to implement classes able to provide these numerical features. These interfaces are discovered automatically by SciJava discovery mechanism. These are:
  • org.mastodon.revised.mamut.feature.SpotFeatureComputer and
  • org.mastodon.revised.mamut.feature.LinkFeatureComputer. There are some examples in the same package.
• A calculator class is in class or registering these computers, managing their dependencies, and feeding the Model with the results: FeatureComputerService with concrete impl. DefaultMamutFeatureComputerService.

UI.

• A GUI panel shows to the user what feature computers are available and let them select the feature they want: org.mastodon.revised.mamut.FeatureComputersPanel

To discuss.

• [ ] This PR imports SciJava and friends logic to the project. We probably want to make sure we do it in a better way than proposed now.
  • [ ] It is probably a good time to also discuss feature serialization / deserialization, which is not touched by this PR.