Webapps: maintain the session cookies for the user session
Instruct Oxide to store/load the session cookies on disk in a per-webapp directory under XDG_RUNTIME_DIR. The first time in a user session that the webapp is launched, the session cookies (leftover from previous sessions) are not loaded, but only stored (this is the chrome's "persistent" sessionCookieMode). The next times, session cookies are both loaded and stored (chrome's "restored" sessionCookieMode).