implemented Show.get method

* although it's implemented it's a poor implementation due to the number of
queries that need to be run. this is due to the last_viewed date part of the
method. the number of queries that need to be run will be the same number as the
number of episodes in a show. this would mean that if the search terms result in
a high number of shows and --no-limit is set then we're pretty much screwed.