Many Under the hood changes

[marcelgerber]

This PR includes many Under the hood changes, like (not in a particular order):

• Important XSS prevention (unfortunately, we don't have anything better than $("<div/>").text(var).html() right now, but that's gonna do it)
• Remove the Starter Issues/Features dummy content (just like we did with the New Features content before) and show a spinner instead
• Remove those goddamn .DS_Store files and add a .gitignore to exclude them
• Use more jQuery style (makes everything easier and looks nicer) and Deferreds + handlers
• Adapt the Brackets code style/coding conventions, at least a little (mostly about indentation, spaces and " vs ')
• GitHub API (starter issues): Tell the API to only deliver 6 bugs at max, so that we don't need to handle slicing it ourselves
• Retrieve the count of languages Brackets has been translated into and put into the Contribute page's section about translating
• Use some ECMAScript5 features like Array.forEach and Array.some. That won't work in old IEs, but that's not an issue according to https://github.com/adobe/brackets.io/pull/67#issuecomment-42252995
• Use RegExp.test() for OS testing
• Remove non-necessary duplicate #blogposts container

If you don't like any piece listed here, ping me If you don't know what a particular piece of code is for, ask me

Thanks.

Demo: https://dc7296e2001a9014f1d00ea89b966216336fe5b7.googledrive.com/host/0B986Uw1nLGY7XzNlY2hXVXI5X1U/index.html

[ingorichter]

Except for the warning about mixed content loading, which has been there before, everything looks good so far. I'm going to merge this PR. Thank you @MarcelGerber.