UI adjustments for mutually exclusive (radio button version) encipher/decipher-only Key Usage #664 (#692)

* UI adjustments to make Key Agreement, Encipher Only, and Decipher Only relationship more user-friendly

* whitespace typo

* Issue #663 switching Encipher/Decipher Only options to be mutually exclusive and un-checkable radio buttons.

* Found a bug in the fields schema that was dropping Key Agreement bit if encipher/decipher only weren't checked

lemur/common/fields.py

@@ -162,6 +162,9 @@ class KeyUsageExtension(Field):
             elif k == 'useCRLSign':
                 keyusages['crl_sign'] = v
 
+            elif k == 'useKeyAgreement':
+                keyusages['key_agreement'] = v
+
             elif k == 'useEncipherOnly' and v:
                 keyusages['encipher_only'] = True
                 keyusages['key_agreement'] = True