Always use server 'default' embeddable page

See:
https://groups.google.com/forum/?fromgroups#!topic/lab-models/RliBshPR9BY
Test whether model runs without any errors and try to avoid 'false alarms'

E.g. by stopping model right after loading (some of them are started
in 'onLoad' scripts).
Update reference screenshots (Lab 0.9.0)

[#68727994]