Introduce "discovery template"

[fabiocarvalho777]

Introduce a template whose goal is not to transform an application, but rather only gather metrics, meta-data and information about it.

This type of template must only allow utilities on it, and could be used to learn about an application, and store that knowledge in persistent transformation context attributes (see #305 ).

This feature will require major refactoring changes. For example, the transformation engine should be named something else, since now it might be used not to change an application, but also to just gather information about it.

Also, transformation operation should not extend transformation utility anymore, since they are now very different (this feature and #305 requires TO to not be TUs anymore, there must be a clear distinction between them). It should extend of some sort of "execution unit" class. Having said that, this issue depends on #199.