v1.5.0 -parity with internal SDK

[cristobal-buenrostro]

Latest internal SDK versions (0.7.1 - 0.7.3) applied to public.

• Add option to specify the launch mode.
• Add option to load Immersive Reader in an Edge Webview2 desktop application.
• Add option to run a callback function when Reading Practice message is available.
• Add readerReadyDuration property in the launch response.
• Add gcmCorrelationId property in the launch response.
• Add launchDuration property in the launch response.