add okhttp and okio jars
use okhttp for thetvdb.com requests

it makes the code slightly simpler, is more efficient, and is more
resilient. and it caches requests which will hopefully greatly reduce
data usage.
bump min sdk version to 9

needed by okhttp.
Merge branch 'okhttp'
display episode dates in episode list
change date formatting in episode details

use the long formatting (use full month names), and display just the
date instead of prefixing "First aired: " to it.