feat(usage stats): add one-time stats report sending

Stats are something we need in order to target distributions, architectures, versions, etc that needs improvement in packaging, dependencies, etc.

It also permits to have an overall idea of how many times Ricin got installed. Here are some ideas discussed in #tox-dev to find the best but also the securest way to do this.

• Ask the user if he wants to send anonymous statistics via a secure way in order to help us improving Ricin. Sentence has to be clear and MUST be translated in every language we supports.
• Make it clear about what are the data being sent: Ricin version, OS, Distribution + version, Architecture, Window Manager + version, Ricin's dependencies versions.
• Send stats using a simple bot, to prevent use of HTTP that may leads to data leaks.
• Use friend requests to send statistics, as friend requests go through the onion, they can't be intercepted/known by TLA.
• Make the statistics public on the Ricin.im website.

Note: This proposal is probably missing points, feel free to point me out what I should add/edit/remove.