Addresses Static Web App deployment issues (Azure#85)

Address a few different Static Web App deployment issues

- Deprecates usage of swa login. Will now manually query for deployment token and pass via --deployment-token param of swa deploy
- Defaults to default environment name regardless of azd environment name till Enhance static web apps endpoint listing with support for multiple environments. azure-dev-pr#1152 is resolved
- Adds deployment validation check to ensure environment is in "Ready" state
- Now works correctly in Linux based hosts

README Edits for going live (Azure#37)

* Edits for going live

* Move uninstall instructions below install instructions

Update vscode extension link (Azure#52)