Fixed: continue playing next song if an error happens during the current one

There seem to be some files that (at least on my phone with Android 4.4) always
generate an error what=1 and extra=-1004, and more often if you seek within
the song.I consider this a bug in MediaPlayer, but nonetheless, we should just
move on to the next song instead of hanging to the current one.
Library view, swap behavior of main item and arrow: main item expands, arrow plays.

I find this more intuitive, and I plan to replace the "arrow" icon with a "play" icon.
This is my personal preference, but I find it more intuitive because it is similar to
most other players.
Now playing queue: don't close on click, and do nothing on long-click.

Doing nothing on long click allows to "cancel" a click if one puts their
finger on something and changes their mind: just hold on to long-click out of it.

Not closing (finish()) on click is useful for quickly scanning/browsing:
"was it this one?" ... "oh, wait, maybe this one" ... "no, let's play this other one instead".
It's annoying to have to re-open the view each time in this scenario, and since the
long click is not available anymore for this, and I personally don't see the point
anyway, we just keep the view on when we get a click.
Show play icon instead of expand arrow, since the behavior changed.

TODO: the description string needs to be changed too.
Also, the icon looks too big, needs to be scaled down a little.