Create a migration doc covering changes from `alpha` & `beta` to stable v4

[sesemaya]

Document the breaking and the most notable changes for people who update Material to stable v4 from alpha or beta:

• FAB with dropdown menu
• Navigation drawer variations with responsive behaviours
• Textarea auto resize removed
• Waves removed

[djibe]

Thanks.

[djibe]

Textarea autosize is here ;-) https://jsfiddle.net/djibe89/bofcrp8v/

[sesemaya]

Migration doc: http://daemonite.github.io/material/docs/4.1/getting-started/migration/