Load movie lists in parallel

When loading movie lists a lot of the time is spent waiting for IO when
loading meta info. When the info for one Movie is received we go on to
the next movie in the list and get meta info for that movie.

This commit will get meta info for all movies in parallel instead. Since
most of the time is spent waiting for a response, we might as well wait
for all of them at once.

To test the effect of this patch I removed all locally cached content before each execution to get a worst case scenario where all the info has to be downloaded.
Without this patch it takes more than 2 minutes for me to load "People Watching"
With the patch it takes less than 30 seconds to load "People Watching".

There are other parts that can be changed in a similar manner, I'll be happy to make more changes if you want them.