Add missing elements: estimated_[raw|compressed]_size

We found the "estimated_[raw|compressed]_size" elements to be missing in appliance.xml as well as appliances.xml. They seem to be returned from real servers in any case, as far as I can see.

By the way: Can we expect that the returned value is always a string with the "MB" suffix? We were trying to parse it into a number, see this [commit](https://github.com/susestudio/susestudio-lib-java/commit/926f051f28f82cfe5d64cc8e1786f0d679719828).