luci-base: luci.js: further nested Class.super() call fixes

Use stacks keyed by class id + symbol internally to not clobber the
prototype scope pointer when repeatedly calling super() in invoked
methods.

Ref: https://github.com/openwrt/luci/issues/3316#issuecomment-558531111
Fixes: 374c23cd

 ("luci-base: luci.js: properly handle nested Class.super() calls")
Signed-off-by: Jo-Philipp Wich <jo@mein.io>