Optimize Flash component

[Terris]

Now that Flash is fully integrated I'm already seeing some ways it could be optimized (of course). This PR serves to make those optimizations.

• Add appropriate dependencies to useEffect.
• timeout functionality should only result in visual changes and not cause an unnecessary render.
• visual timeout should not be a jarring flash - now it's a slide up.

[thedavidprice]

@Terris FYI, we just flipped the default from 'master' --> 'main'. #718

Wanted to make sure you knew!

[Terris]

@Terris FYI, we just flipped the default from 'master' --> 'main'. #718

Wanted to make sure you knew!

Aha, I missed that. Thanks for the heads up.

[peterp]

Hey @Terris, I'm busy running through our e2e tests for the tutorial and I'm getting an error message that "viewed" is undefined.

(This occurs when I click on the delete button after creating a post.)

Is this something that you know about, and is covered in this PR, or would you like me to open a separate issue for this?

[Terris]

@peterp Dang, I'm not able to reproduce the error you are seeing. Is there any further log info that might prove useful?

[peterp]

@Terris Ok, no problem, I'll try to reproducce it outside of Cypress and I'll open a ticket.