[Enhancement] Add a confirmation box (that shows the tweet) when retweeting

[Contribucious]

Would be cool to have a confirmation box when we click on the Retweet icon.

=> See screenshot: http://i.imgur.com/8Et7jh4.png

Because, even if it's specially useful when we've a desktop client that uses the streaming API and therefore have the timeline being (very if many following) often refreshed, still, even with a client with a refresh rate set to 2 minutes for example, it can happens. What? Retweeting a bad/undesired tweet! Because the time we spot the desired tweet we want to retweet and click on the Retweet icon, a timeline refresh may have already occurred! Even if the probability is low in contrast to desktop clients that use the streaming API system (btw, as Birdie one day we can be sure eheh, so… specially useful for the future but already there —and already useful too— like so). And the icon clicked behind our mouse cursor becoming the one of an other tweet (that can even be an embarrassed one that we never wanted to retweet! and even with a quick canceling, too late, everybody or almost who were there on Twitter will have a notification for sometimes 10 secs, via Growl notification for Mac users, via the notify-osd system for Linux users typically, etc.).

That's probably for that reason that many desktop clients have this behavior!

Also note that the confirmation box therefore includes the tweet content to be sure about the tweet that we are about to retweet so, as it's the goal here eheh. Not just having a YES/NO confirmation dialog, which is not really useful in our case.

TECHNICAL INFORMATION:
OS: Ubuntu 12.04.2 LTS (with Cinnamon)
Birdie version used: the r244 from the DAILY repository