drafts: Improve logic to add/remove/ignore.
drafts: Improve logic to add/remove/ignore.

*If draft === message, then ignore.
Either both are empty or user changed nothing in the
previous draft.

*If message.length === 0, then remove draft as user have
cleared the message.
*else update draft as user have updated message.

Fix draftRemove action is always fired when chat screen pops.

vishwesh3/zulip-mobile,vishwesh3/zulip-mobile,vishwesh3/zulip-mobile,vishwesh3/zulip-mobile