Nouveau string refinement

[boonebgorges]

I've noticed a few places in Nouveau's new strings that could use a small amount of refinement. I'll use this ticket to track the changes.

[boonebgorges]

In 12017:

Nouveau: String improvements for group invitations.

See #7786.

[boonebgorges]

In 12018:

Nouveau: More consistent capitalization in group invites nav.

See #7786.

[boonebgorges]

In 12019:

Nouveau: Improved language in groups AJAX callbacks.

See #7786.

[boonebgorges]

In 12020:

Nouveau: Language improvements in functions.php.

See #7786.

[boonebgorges]

In 12021:

Nouveau: String improvements related to private messages.

See #7786.

[boonebgorges]

In 12022:

Nouveau: Improve string in messages AJAX.

See #7786.

[boonebgorges]

In 12023:

Nouveau: Improve escaping and avoid markup in translatable string during AJAX update posting.

See #7786.

[boonebgorges]

In 12024:

Nouveau: Use correct i18n for group invite failure message.

See #7786.

[boonebgorges]

In 12026:

Nouveau: Correct punctuation in group creation header.

See #7786.

[boonebgorges]

In 12027:

Nouveau: Improved wording for message star/unstar feedback messages.

The previous technique for using sprintf() to build the message was not
i18n-friendly.

See #7786.

[boonebgorges]

I've done a sweep through and changed all the instances that caught my eye. Let's leave this ticket open until the next beta. If nothing else has been spotted by then, we can call it fixed.

[boonebgorges]

In 12046:

Nouveau: Some language improvements for Customizer group settings.

See #7786.

[boonebgorges]

In 12047:

Nouveau: More Customizer string improvements.

See #7786.