Use more css and phorge standard elements for application view

Summary:
This diff streamlines the application view. This includes:

• using the newPage method of the PhabricatorController
• using the application crumb standard class for rendering of crumbs
• using 📊 as application glyph
• using css and flex for sizing of the drawio app iframe (circumvents magic css numbers)
• implementing some phorge coding standards

Test Plan: Creating and editing diagrams (and older versions) look at the new breadcrumbs. Is everything looking and working as expected?

Reviewers: mturdus, valerio.bozzolan

Reviewed By: mturdus

Subscribers: valerio.bozzolan, mturdus

Tags: Diagrams (Extension), Arcanist

Differential Revision: https://we.phorge.it/D25612