Add auto-scrolling to st-scroll-view.

[mtwebster]

• It must be explicitly turned on via set_auto_scrolling method.
• It defaults to on in the Menu applet, selectable in Cinnamon Settings
• Establishes a region to the top and bottom of the StScrollView
  that overlaps slightly in the view itself, and mostly above and
  below the view.
• Speed scales across entire region of scrolling from very slow to very fast
• Only vertical scrolling is supported at this time
• Scrolling stops of your horizontal position moves outside the
  bounds of the scroll view, or you move up or down out of the
  scrolling region
• Initiation of autoscrolling can only happen directly inside the
  scroll view (the extended regions are not sensitive until you've
  triggered autoscrolling within the original view)

[KevinLarsson]

Brilliant! I've been testing this feature for some time now and it works perfectly. Thanks @mtwebster .
Please, consider merging it.

[Garibaldo]

Auto-scrolling would be a very nice addition to Cinnamon main menu. I hope it will be included in the Lusito's menu overhaul.

[mdchaves]

This feature would make much easier navigate through the menu, especially if you have many programs installed and if you are mostly a "mouse user", as most people. We would save a lot of extra clicks and mouse scrolling. Some people that are mostly "keyboard users" might not realize how useful this feature would be for everybody else. I also hope this pull request get merged.

[cesar404]

Amazing! Cinnamon menu surely needs something like this. I understand that it is optional, so those who don't like it can turn it off. I strongly support this pull request.

[AlbertJP]

This pull request doesn't cleanly merge, please rebase it.

[ScipioAfricanus]

Awesome! This is very useful when you have a great amount of software installed on your system and you have to browser quickly across the huge list of applications on the menu. Using mouse wheel or scroll-bars are certainly not the best way to do so. I much prefer the auto-scroll feature implemented in this pull request.
Every single decent menu that I know has a feature like this. For example: Windows XP start menu, XFCE main menu, LXDE main menu, Gnome 2 menu, Mozilla and Chrome bookmarks menu, ClassicMenu indicator and so on...
Even Unity Laucher has auto-scrolling.
I hope it gets merged soon.