[web] Move accountPassword state up from ThreadSettingsModal to ConnectedThreadSettingsModal

Summary:
Move accountPassword out of the inner class component state, and move it out to the wrapping "Connected" functional component.

As part of the work to refactor ThreadSettingsModal… specifically to turn it into a functional component.

Depends on D3756

Test Plan:
Close reading... should be a noop

Will test the entirety of ThreadSettingsModal thoroughly once the refactor is complete (plan on using this as an opportunity to write some automated tests)

Reviewers: palys-swm, def-au1t

Reviewed By: palys-swm

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

Differential Revision: https://phabricator.ashoat.com/D3757