luci-base, luci-lua-runtime: fix "dispatched" and "requested" properties

Ensure to properly emulate the "dispatched" and "requested" properties
which refer to the executed and initially resolved menu node respectivey.

Also stop exposing a `node` property in Lua context to maintain full
compatibility with the old Lua runtime.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>