Improve the visual representation of the data model

[stefjoosten]

The data model generated by Ampersand can be improved on several counts:

• As a programmer, I'd like a command ampersand datamodel to shortcut the command ampersand documentation --format docx --no-text and to avoid generating way too many unneccessary diagrams.
• The small boxes that are not an entity should be treated as entities when drawing the data model, so that they are drawn within the boundary of the pattern in which their ConceptDef resides.
• Aliasing is currently drawn erroneously. Suppose CLASSIFY A IS B must be drawn such that both A and B are visible, but are clearly aliases of one-another. (Look at the definition of A_Concept in AbstractSyntaxTree.hs.)

[hanjoosten]

Example of the "small boxes" that are drawn outside the pattern boundary. This is ugly so that makes point two (above) more plausible.