fix: Separate remove button into own controller

[thevoiceofzeke]

This is a conflict-free version of #699

In this PR:

• Broke functionality for widget remove button into its own controller
• Replaced jQuery stuff with angular filters or plain javascript

Why?

The functionality used to live in LayoutController, and every instance of a <remove-button> in a user's layout was causing LayoutController to initialize (including the getLayout() service call. It's probably better if each instance of the remove button only initializes what it needs to function.

Proof that it still works

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[davidmsibley]

love it.