Convert PeopleSpaceActivity to Kotlin

This CL converts the PeopleSpaceActivity to Kotlin. This is so that
ag/24308773 can call coroutines extension functions, which look
extremely bad when called in Java.

This is a pure conversion with no change in logic.

Bug: 238993727
Test: Manual, built and started the PeopleSpaceActivity by adding a
Conversation widget to the launcher.
Change-Id: Id5e94ce517111d503a7e48576891d7b7680835e3

Change-Id: Id8eeac2b5dd52849b85f9e92c7e052987507451c