Make data synchronization more efficient

[freezy]

Right now, importing 1200 artists and 500 albums takes about 10 seconds on a Nexus S. This seems pretty slow. The current algorithm is as follows:

• Read HTTP body into a String buffer
• Use JSONTokenizer to serialize it into a JSONObject
• Loop through the JSONArray of the response
• INSERT each item (ON CONFLICT REPLACE constraint on the ID will remove duplicate entries)
• DELETE items with timestamp < current time

It's probably faster to just update current entries. Ideas in the comments.

[freezy]

Done by smee204, cheers!