Hack in support for multiple servers and retry logic with concurrent downloading.
Update protobuf-net to 2.0.0.668 to match SteamKit2 update.
Revert "Use console instance when possible. (now caches user sentry data and steam id to config.vdf)."

This reverts commit e96e8bae516a95f346269d545ec0719236f50766.
Misc cleanup.
Ignore "depotfromapp" depots for now.
Connect to eight servers instead of six as very often first few will not be usable.
Update SteamKit nuget package to 1.5.0.
Fix protobuf-net reference.
Fix potential collision when creating directories. Remove staging files from unclean exit.
More cleanup:
- Don't calculate matching chunks if file hash matches (now that related SK2 bug is fixed).
- When file doesn't already exist, set length immediately after creation.
- Remove redundant file existance check before copying existing file to staging.
- Normalize more var names.
- Print account name for which password is asked.