Revert "Revert "Compress all activity-object properties of an activity""

This reverts commit 2ffebf5121ad45628e16af0f2cc16d17e902a7b3.
Revert "Revert "Ensure objects with just an URL""

This reverts commit 93f4c2a76cb70ed4ed3f5dc737aaca3706152589.
Whitespace
Put better debugging info into ActivityObject.expandProperty
Add a toString() for activity
Automatic upgrader for activities