overview: fix huge memory leak of views

Each time the refreshThread refreshes the overview panel data a new
listview object would be created. Obviously this causes a huge memory
leak after a certain amount of time and dumpsys meminfo com.aero.control
would show insane values (up to 15.000 View Objects after two minutes).
Those views will never be cleaned up by the GC and thus Aero Control
creates a bug memory leak.

Solving this was actually very simple; instead of the ArrayAdapter
object, we give the ArrayAdapter now a list full of those objects. This
allows us to override clear() and notifyDataSetChange() which are both
needed here.
The actually view counter number went down to about 100-200 on normal
startup which is very nice.

Notice: The same "issue" could be also found on the cpu statistic panel,
but since we won't refresh data here its not a big deal. For future
stuff we should consider GC doesn't always clean up as expected.