Add redirect to support RFC 6764 (".well-known" addresses)

I added a bit of code to support an HTTP 303 redirect to base_prefix when a client requests /.well-known/carddav or /.well-known/carddav. It's been a while since I've touched Python so feedback would be appreciated. I tested on iOS 7 and it worked great as long as you pre-create an address book and corresponding props file with {"tag": "VADDRESSBOOK"}. iOS then seems to pick up the availability of the address book automatically. I tested with multiple vcf files too and they were both selectable under "Groups" in the Contacts app. I also tested on an Android (4.3.1) device with Card/CalDAV-sync (0.4.5 and 0.4.1, respectively) to make sure I didn't inadvertently break anything and all seemed to be work fine, both when specifying the full path to the address book and when using only the domain name ("https://example.com:5232").