Fix for the bug 990481

I agree that since we'll have public ```lock\unlock``` methods we can make ```lock``` as "private" and move it to ```state``` (eg. like we do with ```resizing``` https://github.com/azasypkin/gaia/blob/0f93196939e02a559ed23ca4ade6301d3bc9a7de/apps/sms/js/compose.js#L47)