Slim Recents: fix toptask header layout and other ui improvements

1) For the toptask, we can keep the expandButton imageview so the layout
doesn't get broken (the app title gets centered while other cards have
left aligned title, and the app icon gets bigger than other cards - it's
more noticeable when you set a small panel size like 75%) and just set
its alpha to 0 so it's not visible anymore.
At the same time, we can avoid the click listener creation for this case,
avoiding useless listeners is always good.

2) add a bit of padding for apps icons

3) make header longpress app info icon white like other longpress icons

AICPfy:
Keep padding exposed for themes

Change-Id: I887fb347bed5603eb0a345ea3a5202ca04b62f82