Fix of minor Android doc issues and addition of new Android migration guide

Here's a pull request for 2 items that I have worked on. My first commit 79866ad fixes some issues with the Facebook integrations docs on Android. My last commit ea4f7e1 adds a new section to the Android guides, a migration guide.
There's a 3rd commit e8b2e50 in the middle that resulted from a merge of the latest changes of the repo. That's not my work, please disregard that big commit