prepare for SaaS

[21pages]

1. Add email in LoginRequest to identify the control side.
2. Add salt in LoginRequest and support_controlling_salt in Hash to support new password verify flow.
3. Use appname to distinguish between standard, client, host, and possible SOS versions.
4. Add STRATEGY_OVERRIDE_SETTINGS for override advanced options, add STRATEGY_HARD_SETTINGS to support hard settings like custom client.