add ability for embedded library to replace help function

[balmas]

Per discussions with @abrasax

We would like for the alpheios nemo application to be able to have the help button on the floating toolbar open the popup Getting Started help, rather than the help on the panel.

This change will also make it possible for other sites using the embedded library to override our help with their own, should they choose.

[balmas]

qa-3.0.0.54/components 1.2.22

test this the texts-test environment, which makes use of the new feature. See alpheios-project/alpheios_nemo_ui#258

[monzug]

I am not sure how I can test the second part
This change will also make it possible for other sites using the embedded library to override our help with their own, should they choose.
any idea?