enhance quota mechanism for per-tenant

Now, Glance use config option to achieve quota check. But it can only set the quota with the same value for all tenant. It includes tags,properties ,locations and storage quota. We can't set different value for different tenant. And there is no image number quota as well. The function is limited.

As I know, the db quota mechanism has already been Implemented in Nova,Neutron and some other projects. To consider deeply, I think it worth to introduce the db way to Glance. Using the db way, we can set different quota for different tenant. The quota management will be stronger and more useful. And the image will be managed more convenient.