Lemur cryptography refactor and updates (#668)

* Renaming the function so it sounds less root-specific

* Refactoring lemur_cryptography
* Adding to the certificate interface an easy way to request the subject and public_key of a certificate
* Turning the create authority functionality into a wrapper of creating a CSR in the certificate codebase and issueing that certificate in this plugin. (Dependent on https://github.com/Netflix/lemur/pull/666 changes first)
* Ensuring that intermediate certificates and signed certificates retain their chain cert data

* Handling extensions that are the responsibility of the CA
Implementing authority_key_identifier for lemur_cryptography signatures and including skeletons of handling the certificate_info_access and crl_distribution_points

* Fixing errors found with linter

* Updating plugin unit tests

* Changing this for Python3. Underlying cryptography library expects these to be bytes now.

* Updating tests to match new function names/interfaces

* Another naming update in the plugin tests

* Appears that create_csr won't like this input without an owner.

* Undoing last commit and putting it into the right place this time.

* create_csr should be good now with these options, and chain certs will be blank in tests

* This won't be blank in issue_certificate, like it will in creating an authority.

* Much cleaner

* unnecessary import

lemur/certificates/models.py

@@ -200,6 +200,16 @@ class Certificate(db.Model):
     def validity_range(self):
         return self.not_after - self.not_before
 
+    @property
+    def subject(self):
+        cert = lemur.common.utils.parse_certificate(self.body)
+        return cert.subject
+
+    @property
+    def public_key(self):
+        cert = lemur.common.utils.parse_certificate(self.body)
+        return cert.public_key()
+
     @hybrid_property
     def expired(self):
         if self.not_after <= arrow.utcnow():