Project migration (#198)

* Docs: redirect to new website

* Docs: rename docs -> docs-legacy

* Revisit README.md

* Review github workflows and secondary markdown files

* Review build files

* Fix demo app and tests

* Multiplatform publications

* Idea files

* Docs migration

* Fix emulator runtime

* Fix deployer dependency

* Min SDK version bump to 21

* Enable emulator stacktrace

* Read signing info