Allow for certificates to be re-issued

[kevgliss]

It is often useful to allow users to easily re-issue their certificates. The way I see it there are a couple different ways this could be implemented:

• Force issuer plugins to implement a 'reissue' function
  • Each CA does reissue a bit differently, Symantec/Verisign has it's own logic on what it means to reissue a certificate. We could force issuer plugins to create a reissue function that would navigate the logic of that particular CA. The messy part is that CA's may require that a state or challenge be saved and then presented before a certificate will be re-issued.
• Save the request data when a certificate is created
  • If we save this data (json) Lemur's re-issue function might be able to simply use the same data and modify the not_before, not_after values (maybe OU?) then create a new certificate using create_certificate interface. This is much easier to implement but a major drawback is that we don't know what the rules are in determining if a given certificate already exists.

[kevgliss]

A third way would be to parse the certificate fields and extensions and return such that this information could then be fed back through the process (with new dates) and have a new certificate issued.

This would also allow us to edit the 'cloned' certificate if need be (e.g.) adding a new domain.