Fix broken version label in About dialog

[HebaruSan]

Problem

The About dialog's version label no longer shows the version:

Cause

The labels on the About form all have hard coded sizes and are not auto-sized, and the version string is longer than it used to be (build number was added), so the version label is wrapping and then being truncated vertically.

Changes

• Now all the of the About dialog's labels have AutoSize = true, so they'll always show their full contents
• Now if you press the menu key while focused on a link label, the menu will appear under the link label instead of at the mouse cursor

Fixes #4276.