new playstore-screenshots.py script, to take screenshots on different devices / different languages
open notifications and reader
open media library
list devices and take screenshots on all connected devices
open post editor, type text and open virtual keyboard
new README.md
use a thread pool for concurrent run
Revert "use a thread pool for concurrent run"

This reverts commit 0aa16b4c9490abf1c8d3632a7bce2c28213a0711.
fix typo
add adb prerequisite and run example
use shell mode in Popen call
Merge pull request #2104 from wordpress-mobile/issue/playstore-screenshots

New tool to take localized screenshots on multiple devices/emulators