Add font smoothing to icon font in table header of support forum

[zodiac1978]

On the support forums bbpress is changed in some way. For example the table header for the counts (replies and voices) are now icons instead of just text.

But these icons don't look good. A little bit "smudgy".

I think they are missing some font-smoothing.
​https://davidwalsh.name/font-smoothing

If you add this CSS ...

	-webkit-font-smoothing: antialiased;
	-moz-osx-font-smoothing: grayscale;

... the icons look much better.

These are the selectors which need the CSS:

.bbpress .forum-titles .bbp-topic-voice-count::before 
.bbpress .forum-titles .bbp-topic-reply-count::before 

Maybe there are more icons which could need some font-smoothing. This is just the first occurrence I saw.

[zodiac1978]

Without the CSS - this is the status quo.

[zodiac1978]

With CSS - this would be the new appearance of the icons.

[zodiac1978]

First patch to fix just the mentioned icons

[zodiac1978]

Fixed typo

[SergeyBiryukov]

In 8172:

Support Theme: Add font smoothing for Voices and Replies icons in topics table header.

Props zodiac1978.
Fixes #3997.