Expands leasedb tests
Removes BucketCounter from storage.py
Removes BucketCounter from web/storage.py
Removes BucketCounterTest
Removes BucketCountingCrawler class
Adds test_stats to test_storage.py

This is used to test the new bucket_count reported by the server,
as well as the new stats total_leased_sharecount and
total_leased_used_space.