Add support for Material theme and release 1.1.0.alpha1

[Artur-]

Needs a Material theme class similar to com.vaadin.flow.theme.lumo.Lumo

Probably depends on vaadin/vaadin-material-styles#49

[pleku]

Acceptance Criteria

• There is a material theme integration module in Flow
• When the material theme has been added, we release Flow 1.1.0.alpha1 with the material theme module
• We add documentation about material theme being available to the users in addition to Lumo

Once all the flow and all the components have been released as 1.1.0.alpha1, we add/update the dependencies to the V11 platform

[SomeoneToIgnore]

Material theme support had been added in #4322
The documentation needs to be added.

The documentation is not added, since the support is not available for testing: due to the issue described in webjars/webjars#1781 it is impossible to publish current prerelease Vaadin WebJars: we either need to wait until the issue is resolved or change the bower.json in all components with Material theme support.

[SomeoneToIgnore]

Documentation is added in: #4238

Now the release is what's left to be done.