Download CEF builds from S3

Story https://trello.com/c/1JK3Ordd

Changed the download URL to get the CEF builds from S3 instead from dev.brackets.io.
Added task to download the symbol files for the CEF version that we use to build Brackets.
That is more a reminder... I couldn't find something to extract the 7z file when I implemented this feature. I found something last night that I's like to give a try and see if it will extract the 7z files.