Fix the Options menu UI

[guillaumealgis]

This is a small UI improvement for the Options menu.

• Adds a down arrow on the right of the cog icon to make it clear the button will display a dropdown menu
• Fix the indentation of the menu items to match the other OS X dropdowns
• Move the version label to the menu

The reasons for the version label move are:

• Most users don't care which version of Alcatraz they're using...
• ... and if they do, they can still find the info easily. But always showing the version number is not necessary.
• It makes space in the window, which I intend to use to display loading and error indicators (for Cache package list #325, amongst others)

Here's a before / after, and an OS X dropdown for comparison:

[jurre]

👍

[supermarin]

👍