Addition of unzip (for windows), bird and cloud options. LT5 and LT7 download capability

I added the following options:

 - z - to unzip downloaded tgz files. Uses the tartool (https://tartool.codeplex.com/)
 - b - which lets you select the product you're looking for (LT5, LE7 or LC8)
 - c - which lets you define a cloud cover limit for the downloaded images. If an image is found whith clouds below the limit the script stops looking for more images within the time interval. If not, it doesn't keep the image and tries to find another.

The connection to earthexplorer was established within the while loop, so it was repeating it for each iteration. I moved that block to before the while loop, making the process much faster.