Feature request: Add optional system notifications for pending actions

## **What problem are you trying to solve?**

I'm buying HEX now. Metamask works fine, but I don't. Every time I click on the buy button on the website, it goes into "pending" forever until I remember that Metamask has to approve the transaction. The only clue is a very tiny "1" that appears on the very tiny Metamask icon in my add-ons tray. If I had the add-ons tray minimized, I wouldn't even see that.
The last couple of times I've used it, the "1" doesn't even appear. I just need to know to click on the Metamask icon.

## **Describe the solution you'd like**

I would really like an option for Metamask to pop-up a normal (big) system notification reminding me that I need to do something.
In any case, I would like some obvious visual cue that an action is required.

## **Additional context**

I am using Metamask with Vivaldi 2.10.x on kubuntu 18.04 (KDE).

The report names no files, tests, or entry points; start by locating the code that leaves a website buy action pending. Define the optional system notification and the requested obvious visual cue, then verify that both communicate when MetaMask approval is required.

Written by the indexing model from the issue text.