Add (slightly better) mobile support for comments

[Ninjaclasher]

In particular:

• Less indenting for small-width screens
• Decreased gravatar width for small-width screens
• Use flexbox instead of float:right; to make the admin controls display nicer.

Everything should look exactly the same on a computer screen.

Before:

After:

[codecov-commenter]

Codecov Report

Merging #1455 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1455   +/-   ##
=======================================
  Coverage   45.60%   45.60%           
=======================================
  Files         207      207           
  Lines       11885    11885           
=======================================
  Hits         5420     5420           
  Misses       6465     6465           

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[kiritofeng]

I personally am not a fan of the empty space directly below the icon, what if we moved the icon directly beside the username?

[Ninjaclasher]

Something like this?

[Ninjaclasher]

Implemented ^. I'm not sure if there is a better way to do this without having two gravatars (and choosing which one to make visible).

New after:

[Xyene]

Thanks!