Continue modularisation by moving activities in the "About" feature to a
new `feature.about` module.
Implement `feature.about:
- Move `AboutActivity`, `LicenseActivity`, and `PrivacyPolicyActivity`
here.
- Update `markdown2resource` plugin to work with libraries
Implement `core.data`:
- Types and repositories used through the app
- Move `InstanceInfo` and `InstanceInfoRepository` here so they are
available to `feature.about`.
Implement `core.ui`:
- App-specific views, spans, and other UI content
- Move `ClickableSpanTextView` and `NoUnderlineURLSpan` here so they are
available to `feature.about`.
