Make default links to support channels (such as to Telegram etc) for forks be a place holder

Modify `Constants+Credentials.swift` and move URL values like "https://t.me/AlphaWalletSupport" into `Constants` (instead of `Constants.Credentials`). Have a dummy URL for each one and we'll keep the actual values in the copy of `Constants+Credentials.swift` we use for production builds.

Can optionally read from a file like `.credentials` for these for development purposes.

Rationale: So forks don't accidentally link to us for support