If a user has a pre-existing Android SDK location, we install a new one for them automatically. Instead, we should allow them to reuse their existing install, and just update as necessary.
- When a user chooses "Install/Update Android SDK" from the Dashboard, allow them to pick a folder with a pre-existing SDK install
- Validate the SDK installation as per the normal SDK validation process
- If the SDK is not currently up to date, or is missing required pieces, proceed to the update screen.