UI/UX submit button in comment editor should not be right next to the edit issue button

[craigfowler]

In the new "advanced editing functionality" for an issue comment, the button to submit the comment is right next to the button to "edit the issue". This makes it too easy to press it by accident.

What's more, because of the icon for the edit issue button (a pencil) and it's prominence it's actually more eye-catching than the submit comment button.

The problematic side to this is that - if you do click the edit issue button by accident, your comment gets discarded because the app goes to the 'edit issue' screen.

[craigfowler]

Here's an example of what I mean - the buttons in the top right.

[craigfowler]

Tangentially related to #358.

[Tunous]

That's a bug caused by the same thing as #671. This button was supposed to hide when comment editor is expanded.

[maniac103]

@Tunous I fixed #671, but what exactly should make FAB hide when scrolling the app bar?

Edit: It's this check I suppose, which for some reason makes the FAB hide in the PR activity, but not in the issue activity (perhaps due to tabs?)

Another edit: It's definitely due to the tabs; unfortunately I don't see a straightforward way to influence that behavior :-(