Finalize the extra widgets in the canvas

Problem/Motivation

The canvas comes with a few new widgets that are inline to the canvas:

At this point, those provide these features (in the order of display from left to right):

• Model information: opens a config form to configure general stuff about the model, e.g. label, documentation, version, etc.
• Auto-Layout: automatically arranges all objects in the canvas
• Download SVG
• Copy: copies selected element(s) into local storage
• Paste: pastes objects from local storage into the canvas
• Minimap: toggles a little canvas containing a tiny version of the model to easily move around, useful when zoomed in

More widgets may follow, like e.g. zoom-in and zoom-out. Maybe also others.

Each of those widgets should get their own icon. And they should be styled properly.

Proposed resolution

We should use Drupal's icon API for managing the icons, ideally with a set of icons that already exist in core. If not, we have to include them into this module and deliver them packages with it.