Change material imports to one module

[janniclas]

Is your feature request related to a problem? Please describe.

Since we heavily use the material components provided by angular we have to import a lot of these components in nearly every of our custom components. In my opinion these imports clutter the list of imports making it hard to read.

Describe the solution you'd like

In the documentation of angular material the following possibility is suggested as an alternative to single importing every component:
"Alternatively, you can create a separate NgModule that imports all of the Angular Material components that you will use in your application. You can then include this module wherever you'd like to use the components." [https://material.angular.io/guide/getting-started]
This would greatly reduce the number of imports per component making it easier to see what we actually import without all material components clustering the imports.
In my opinion this would be an improvement of code readability. Therefore, I suggest to create a single module importing all material components and including this module in all components, which depend on material components.