Adding bootstrap based template.

I think this is ready to merge now.

For the most part, it is completely responsive. There may be some parts where it doesn't quite work out, and my hope is that this can get worked on into the future. There is some javascript, but the webiste will be just as usable without javascript enabled.

I also added a new string to lang.php for "Past Versions". To fill in the other languages, I used Google Translate. I realise this is not perfect, so you may want to run an eye over the French translation and any other languages you may know :)

I haven't tested the accessibility of it - but it is not the default theme, so hopefully it is not as much an issue as it was with the previous PR. I'm happy to look into any issues people log against it if they choose to use this theme, and then submit relevant PR. But for now, I'm pretty happy with how it all works.