Multiple Changes

Hey, I wasn't sure if you are interested in accepting pull requests, but I made a few changes that I thought might be useful to others:
1. An option to run subscription updates during playback (can be turned off from settings)
2. Added a 30 minute and 1 hr update frequency option. Every 2 hrs is too infrequent for me for TV Shows because a 8PM show may not show up in the library until as late as 11PM. Also changed how update frequency was read so that you don't have to restart XBMC to pick up changes to it.
3. Added logic to only write new strms if the actual content would differ from the old strm. The logic as is was making my library scans take longer than necessary. 

I've been running my updates on my main HTPC for 2 days and my 2 RPi's running openelec for 24 hours or so and everything seems to run as intended.