Add scroll bars for lists

Scrolling through large lists is a drag (pun intended).

Since ionic does not provide scroll bars or other options such as jump-bars quick navigation by itself, need to look for a third-party library or roll our own.

Since ionic itself does not provide these, setting this to "blocked" for now.

After a quick test drive this is the first thing that keeps me from using mopidy-mobile, the search just doesn't replace a good scroll. Seems like Ionic provides scroll bars now.

@notEvil: Where did you get that info about Ionic providing scroll bars? Bear in mind that Mopidy-Mobile still uses Ionic v1, and that will probably not change in the immediate future due to lack of resources...

True, v1 doesn't but later versions (if I'm not mistaken). Nevermind then