@jkandasa your support is outstanding
your example works good and i can use it to build a dashboard to my needs. thank you very very much.

the reason it took me so long to respond is, that i needed to trace a startup error on my end:
[$injector:nomod] Module 'rzModule' is not available! You either misspelled the module name or forgot to load it. If registering a module ensure that you specify the dependencies as the second argument.

symptoms:

• dashboard not loading correctly ({{ variable }} everywhere, nothing works)
• angular throwing error about undefined module
• testing with dev-console on firefox angular.module('rzModule'); yielded no error.
• rzslider.js was actually loaded

cause:

• firefox does not support <link rel="import">
• the polyfill i pushed to github fb3d0d96 is working but:
• too late.

so the polyfill for the import-feature is working, as i am able to load the rzModule after the dashboard html loaded completely and angular tried to load.
but it is not working fast enough.

i am currently trying to find a way to either delay angular startup until all imports are handled or to find a better way to include the /_configurations/additional-headers.html

current workaround: put <script src="https://cdnjs.cloudflare.com/ajax/libs/angularjs-slider/6.6.1/rzslider.js"></script> directly into index.html for firefox

EDIT:
html imports are also deprecated in chrome since v70 and will be removed with v73 which is only two versions from now (v71 as of this writing). see: chrome platform status