Gracefully handle folders with > 2000 photos

[Webreaper]

PicasaWeb has a limit of 2,000 photos per album. Currently, if Picasawebsync encounters a folder with more than 2,000 photos locally, it'll upload 2,000 and then continue to try and upload more, failing each time. Need to:

1. Detect failed uploads caused because the album is full
2. Pre-empt the failure by not attempting to upload new photos into an album with 2k photos
3. Warn the user with a suitable GUI indicator so they know what's happening
4. Optionally auto-split the local folder into multiple folders of < 2000 photos, and then allow them to upload.

[kelvinq]

Hm. Never knew this was an issue. I need to check on this. ;)