Upgrade setup screen to use web framework. (DVPL-4561)

Some workarounds were necessary due to the difficulty of federating between
framework and non-framework views.

Also:
* Upgrade embedded Python SDK to 1.2.3.
Workaround DVPL-4647: Refresh app's configured state after app setup.
Automatically redirect from setup.xml to framework setup view.
Relabel app to just "Twitter" instead of "Splunk-Twitter Connector".
Migrate Twitter credential validation to framework setup view.
Downgrade to regular Django form fields.
Upgrade Tweet Locations view to use Splunk Map visualization.
Workaround DVPL-2401: Index Unicode using unescaped JSON.
Avoid accidentally committing packaged versions of app (i.e. tgz, spl).
Fix Python executable location detection on Windows.
Force Splunk to prompt user to restart after app installation.
Indicate that Tweet Locations view requires Splunk 6.1 to display.
README: Update compatibility information.
Bump version to 3.0.