Remove ant dependency from the core

Most of the work is to be done in package: org.apache.ddlutils.task

Separate classes here into two packages:
1- org.apache.ddlutils.command : contains classes that can be called without ANT ( for example from a servlet). We need to remove the dependency on org.apache.tools.ant.BuildException everywhere in the code. For example create CommandException. Refactor the code to implement Command Pattern method without parameters. Any param to the command, can be represented as state in the class. For example, instead of :

public abstract void execute(DatabaseTaskBase task, Database model) throws BuildException;

We may do:

public abstract void execute() throws CommandException ;

2- org.apache.ddlutils.task : keep ant-dependant classes here, to prepare it to go into another maven project.

Unit testing MUST be implemented against testable class under
package org.apache.ddlutils.command;

and not under package org.apache.ddlutils.task (this will be done in ANT integration).