Improve visibility of dynamic 'Send Invites' nav item

[boonebgorges]

On the group invite page, the 'Send Invites' nav item appears only when you've selected at least one member to invite. This is not totally obvious. I have two suggestions:

1. There's a bug that's causing the 'Send Invites <span>3</span>' count not to be styled. See screenshot. This is an easy fix, which I'll commit momentarily, and goes some way toward making the nav item more visible.

2. This one is more of a suggestion: Perhaps we could style 'Send Invites' in a way that makes it more obvious that it's the next step in the process. I'll mock something up.

[boonebgorges]

In 12025:

Nouveau: Count on 'Send Invites' nav item should be styled.

It was missing the count class.

See #7787.

[boonebgorges]

before [12025]

[boonebgorges]

after [12025]

[boonebgorges]

Screenshot_2018-04-30_20-48-15.png​ is one idea for making the next step more obvious: a light-colored highlight (#eaeaea, lighter than the hover highlight). I'm definitely open to other ideas - or, if others think that [12025] is enough, I could be persuaded of that too.

[boonebgorges]

See #7783, which this ticket might duplicate.

[imath]

In 12040:

BP Nouveau: display the Group Invites UI navigation vertically

On desktop screens, the Group Invites UI navigation is now displayed vertically at the left of the friends/members list or the send invites form. This new position makes it easier to navigate between the different screens and improve the visibility of the send invites navigation item.

Props mercime, boonebgorges.

Fixes #7783
Fixes #7787