[lib] Introduce migration that inserts messageStore.messages into the Client DB

Summary:
When the redux version is bumped:

1. Clear the messages table (just in case)
2. Fill sqlite store with contents of messageStore.messages in redux

Test Plan: Will be tested along with subsequent diffs.

Reviewers: def-au1t, palys-swm, ashoat

Reviewed By: palys-swm, ashoat

Subscribers: ashoat, Adrian, karol-bisztyga, benschac, boristopalov

Differential Revision: https://phabricator.ashoat.com/D2600