Support keyman

Describe the feature
We would like to support keyman both on Windows and Android.

This would require integrating keyman web directly, letting the user lookup keyboards or select a local keyboard file, this should result in a js file for that keyboard being saved into the database, that file will then be loaded into the browser to display the keyboard to the user. This will ensure all users use the same keyboard and by including the js in the project file they will have it even when offline.

The keyboard displayed should be tied to the writing system currently focused.

On Android we will need to figure out how to suppress the system keyboard for inputs which have a keyboard assigned.

On windows we may want to integrate with the windows keyman app, but that's out of scope. For now we just need to have the option to not show the web keyboard as it could get in the way.

The issue names no files, tests, or entry points, so first map the browser keyboard, database, writing-system focus, and Android input integration areas. Define the scope and acceptance tests for loading local or looked-up keyboards, tying them to the focused writing system, offline availability, suppressing Android's system keyboard, and optionally hiding the web keyboard on Windows.