Removed "Upgrading Guides" from homepage

- Dead link
- The "Upgrading Guides" tree was removed in:
  - 15f11a8e1f37f4823a5218989ca08b3bb9f2c026 on 3.0.x
  - 9982d9a019b1c3d1c4f8480b3b054617860d7ee7 on master
CB-3762: change prompt default to empty string

Conflicts:

	docs/en/edge/cordova/notification/notification.prompt.md
Fix incorrect indentations in file examples.

Conflicts:

	docs/en/edge/cordova/file/filetransfer/filetransfer.md
fix imports in android plugin example

Conflicts:

	docs/en/edge/guide/platforms/android/plugin.md
Fix link to CordovaPlugin.java in the Android plugin guide

Conflicts:

	docs/en/edge/guide/platforms/android/plugin.md