Allow stacks to use input parameters

[timgent]

When creating a stack with sensitive information in it (e.g. database credentials) there is no way to pass this in without having it as part of the config file or the template. Don't want to put credentials into these files as they will be stored on github.

Cloudformation allows the use of parameters to handle this situation. Suggestion is to update stacks to support passing in parameters.

[lewismarshall]

May want these to support being input from file (best practice to prevent recording secrets in process list etc...)