Describe the bug
Cannot use 'cp' command while installing it on Windows.
It is needed to replace 'cp' with 'copy' in scripts written in package.json if an user wants to install botfront on Windows machine.

To Reproduce
Steps to reproduce the behavior:

1. Install choco
2. Install meteor
3. Install botfront using meteor npm install in Windows Powershell.

Expected behavior

Here are SSML helper functions that should be extended to covers all SSML features supported by Alexa and [Google Actions](https://developers.google.com/assistant/actions

Current Behaviour

On startup, the media resolver app tries to build an AWS client based on the config values and that fails if they are invalid which results in the app crashing

Expected Behaviour

The app should log that the configuration is invalid and not crash

Example configuration which produced the error

media-resolver:
    storage:
      s3:
        key: "cha