Gui: Control the InReplyTo Header from Composer

Add a QCheckBox in ComposerWindow, that controls whether the current
message will be marked a reply to some other message.

Drafts save/load the state of checkbox. Draft version updated to 3.

REVIEW: 114319
GUI: wrap the message-ids in brackets and support more of them

Also be sure to not cast from QByteArray to QString directly.