Require user to type input to Destroy a stage

[kmanning]

• We've made it really easy to destroy a stage (See: Issue Add the ability to destroy environments through the pipeline #88)
• Perhaps too easy - all you have to do is push a button, and despite the change stage names and text, you're not required to read any of it.
• Let's make it just a tad harder - let's require the user to type in 'destroy <application> <environment>', so that they're consciously acknowledging that they want to take this action, and not accidentally pushing a button without understanding the consequences.