Angular 13 support

[onclave]

After upgrading to angular 13, this warning is thrown during the build process:

⠙ Generating browser application bundles (phase: setup)...Processing legacy "View Engine" libraries:
- angular-gallery [es2015/esm2015] (git+https://github.com/ivylaboratory/angular-gallery.git)
Encourage the library authors to publish an Ivy distribution.

Despite the warning, everything works fine, though.

Thank you for this awesome library, by the way!