Use Kotlin-extensions - todo-mvp-kotlin

I want to add kotlin-extensions to reduce the code, and keep it mutch simple.

The issue names the todo-mvp-kotlin sample but does not identify files, tests, or a specific extension target. Start by locating that sample’s Kotlin sources and reviewing the scope of repeated code before proposing a change. Done should mean the agreed code is simpler through Kotlin extensions, with the scope confirmed by maintainers.

Written by the indexing model from the issue text.