Review / Refine flag language + design

[jenlampton]

Let's take a look at the language on all the flags, and refine as necessary:

• Follow this conversation / Unfollow this conversation
• I found this helpful / I did not find this helpful
• This comment is spam or abusive / This comment is not spam or abusive
• (authors only) Accept this answer / Un-Accept this answer
• (moderators only) This is a Frequently Asked Question / This is not a Frequently Asked Question

We'll also need designs for these flags, maybe some color, maybe some icons? A comparison with what other forums use for these actions might also be helpful.

[jenlampton]

since these have been fine for over a year, closing this issue. We can open new ones in the future as necessary.