One-at-a-time adding issues to epics and related issues

• Adding multiple issues to an epic at the same time is unnecessary.
• It is not a good user experience, and unnecessarily complicates the product.
• We should simplify the design so you can only add one issue at time to epics.
• Also bring the same exact design to related issues, especially since it’s the same codebase.
• So that means we are removing the tokenizing UI.

Design

• Add button is disabled to start.
• When you paste a link to the textbox, the Add button is enabled.
• Clicking the Add button associates the issue with the epic async. And so the button becomes disabled during that time.