feat: prompt confirmation/undo when removing widgets from home

[thevoiceofzeke]

MUMUP-3095: "As a person who just deleted an item from my MyUW homepage, I'd like acknowledgement that I did this and the opportunity to undo it, so I can understand what I did and recover if it's not what I really want."

In this PR:

• Removing a widget can be undone via a toast message
  • Toast resolves automatically after 3 seconds
  • If user clicks "Undo" before resolution, the widget is added back to the layout
• If user deletes another widget before the first toast has resolved, it will automatically resolve it and show a new toast
• On large screens, toast appears in top right of application space
• On small screens, toast appears at bottom of screen (per Material specs)
• Removed unnecessary LayoutController. Expanded and compact modes now share the same layout controller (WidgetController).
• Removed CSS-grid layout in favor of more widely supported flex box
• Updated existing layout controller unit test to test widget controller instead
• Animate widget removal/addition/move

A note about the custom toast message: The toast attempts to follow pattern guidelines for Material Notifications, so it is a custom version of Angular Material's "Toast" directive. All the customizations were made in one commit 9f3b253 to make reverting this work easier, if necessary/desired.

Demos

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Contributor License Agreement adherence:

• [x] This Contribution is under the terms of Individual Contributor License Agreements (and also Corporate Contributor License Agreements to the extent applicable) appearing in the Apereo CLA roster.