Process index and save to database while downloading (not after)

Right now when updating repositories, F-Droid will:

• Download an index.jar file.
• Once downloading is complete, extracts the index.xml.
• Then it parses the index.xml looking for apps and persist them to the database.

If we could unzip the index.jar and process the index.xml file as it is being downloaded, then it should be much much faster. The reason is because saving to the database is slow, but retrieving information from the network is even slower. The CPU and Disk on devices will have a lot of idle time while waiting for network that they could instead spend on saving data to the database.