Unsaved changes dialog

[Liew211]

When editing details, profile, etc, there should be a dialog when the user attempts to leave the page, say "You have unsaved changes, are you sure you want to leave the page?"

[paulbert]

This is pretty broad. Let's start by creating a service and then implementing on one form (MeetupsAddComponent would be my suggestion). Once we've worked out the issues with that, we can implement across other forms that need it.