Improve example deployer to provide full description

[dvojtise]

Motivation

Current GEMOC example deployer plugins directly extract several projects without a clear indication of the future projects names. (ie. only the Finish button is available)
Additionally, the example description on the root page is very short (2 lines), and the additional description lines aren't shown.
Other example deployers (ocl, xtend, ..., and even ale) have enabled a Next> button allowing to have a view of the extracted projects and a larger view of the description.

Proposed Solution

Enable the Next> button in addition of the Finish button with the proposed intermediate wizard page.

Proposed Implementation

Evaluate if we can easily use org.eclipse.emf.common.ui.examples and org.eclipse.emf.common.ui.wizard.ExampleInstallerWizard as in ALE (https://github.com/gemoc/ale-lang/blob/master/plugins/org.eclipse.emf.ecoretools.ale.examples/plugin.xml), in order to deploy our zipped projects (the zip are produced from running project in the git repo.

[dvojtise]

I tested quickly and the org.eclipse.emf.common.ui.examples extension point does support zips in projectDescriptor contentURI, so this action should be straightforward :-)