Single screen session manager

[imsnif]

This changes the session-manager to a single screen, combining the "new session", "attach" and "resurrect" tabs for simplification and convenience sake.

The new screen includes a list of active sessions, followed by a list of resurrectable sessions. Typing a session name fuzzy finds through the entire list, allowing to tab-complete to the first session (and to navigate through the list with the arrow keys).

When pressing if the entered session name does not exist, a new session with this name is created. If it does, we will attach to it, if it exists as a resurrectable session, we will resurrect (and attach) to it.

Those who prefer the previous experience can specify the multi_screen true parameter in the session manager configuration. eg.

plugins {
    // ...
    session-manager location="zellij:session-manager" {
        multi_screen true
    }
    // and/or (same for the welcome screen)
    welcome-screen location="zellij:session-manager" {
        welcome_screen true
        multi_screen true
    }
    // ...
}