Srain 2.0

[SilverRainZ]

This is a Draft PR for Srain 2.0, it may not merged.

Just for the convenience of guys who instered in progress of Srain 2.

I will write a post to intorduce the changes (mostly breaking changes) of Srain 2.0, but not now.

In brief, srain will:

• Move to GTK4
• Use some libhandy widget
• Support GUI configure panel
• Use gobject-introspection to extend its ability
• Support multiple protocols (without define any middle protocol :) )