fixes #6373 - make lifecycle_environment_ids accessible

Smart Proxies can now have lifecycle environments, but when adding a Smart
Proxy through the UI, it fails with a mass assignment error.
fixes #6515 / BZ 1107604 - content host package action: disable Perform on empty input

On "Hosts -> Content Hosts -> [somehost] -> Packages", disable the
"Perform" button, unless the user has provided content in the text
input.
Merge pull request #4339 from stbenjam/6373-proxy-environments

fixes #6373 - make lifecycle_environment_ids accessible
Merge pull request #4398 from bbuckingham/issue-6515

fixes #6515 / BZ 1107604 - content host package action: disable Perform on empty input.