Preparing JDecisiontable 2.3.0

Recently I started to prepare JDecisiontable 2.3.0. This release is intend to introduce the ability to undo/redo actions. I.e. if you remove a rule you can undo this action - this restores the removed rule.

I do this by implementing the command pattern. This means we will not sotre the whole decision table after each action but to store each command. Each command does not only know how to change the decision table it also knows how to revert this change. So we need only very little bit additional memory for undo/redo.

For the command pattern I need to replace writing access to the decision table as well on it's nodes and rules by executing commands. It is necessary to wrap the decision table into a change manager which executes commands and to use read-only interfaces to provide a view on the decision table. Today I released JDecisiontableLib 2.1.0 which has brings the necessary read-only interfaces. Thbis will be the version of JDecisiontableLib used for JDecisiontable 2.3.0.

A part of this work is already done in the branch master including commit c60dae35bc4679f4be08176c8fb9cb3d81a3502d. (See Roadmap.txt) The rest will be developed in the branch version_2.3.0_applyCmdPattern and merged into master if the task is completed.