When the RA mode with StepCAS is used, let the CA decide which lifetime
the RA should get instead of requiring always 24h.
This commit also fixes linter warnings.
Related to #1094
* api/render: initial implementation of the package
* acme/api: refactored to support api/render
* authority/admin: refactored to support api/render
* ca: refactored to support api/render
* api: refactored to support api/render
* api/render: implemented Error
* api: refactored to support api/render.Error
* acme/api: refactored to support api/render.Error
* authority/admin: refactored to support api/render.Error
* ca: refactored to support api/render.Error
* ca: fixed broken tests
* api/render, api/log: moved error logging to this package
* acme: refactored Error so that it implements render.RenderableError
* authority/admin: refactored Error so that it implements render.RenderableError
* api/render: implemented RenderableError
* api/render: added test coverage for Error
* api/render: implemented statusCodeFromError
* api: refactored RootsPEM to work with render.Error
* acme, authority/admin: fixed pointer receiver name for consistency
* api/render, errs: moved StatusCoder & StackTracer to the render package
