Update build-avalon-image.sh

These changes will allow for a better understanding of the formally called --clean argument now renamed to --removeall and the second change will allow that all subsequent builds will automatically be dated the current date that they are built on so no more having to edit this file to change the date for each and every build
Merge pull request #3 from freebitcoinslist/patch-2

Update build-avalon-image.sh