Revert configuration into ember-cli-build.js or use config/icons.js

[bobisjan]

Describe the bug
This add-on uses config/environment.js for subsetting icons and other configuration in the application.

Reproducible test case
Subset icons using config/environment.js, then visit http://localhost:4200 and open the document, the meta tag named {{app}}/config/environment contains list of icons.

Expected behavior
The list of icons is not part of the runtime configuration, the list is provided by ember-cli-build.js or config/icons.js same as add-ons do.

Additional context
Using config/environment.js is not ideal for buildtime configuration like icon subsetting, because the list if icons is baked into the meta tag and served for every request.

[bobisjan]

FYI, using config/icons.js in application works fine 👍.