Bug 829820 - Ability to mark selected SMS thread as Read/Unread

Please note `ThreadUI.onMessageReceived` will also need to markMessagesRead, but in this case you will mark it as unread since you didn't give a parameter for onMessageReceived.

Instead of giving a parameter everywhere, another though is we treat isRead to true by default in markMessagesRead/markThreadRead, it would be fine because the naming of API is 'Read', and treat the isRead is true by default sounds reasonable and you don't have to give isRead: true in parameter, wdyt?