app: Add support for multiple CRLs.

This changes Kedifa.__init__ and Kedifa.loadCertificate method signatures: they now expect filepaths instead of files with a name attribute.

This also changes the (internal ?) Kedifa.crl property in 2 ways:

• renamed to crl_list
• items are loaded CRLs, and not PEM-encoded CRLs. I did not see the point of re-serialising the CRLs after loading if they are anyway loaded again in SSLAuth (the only obvious user of this property)