Bat Míríalta integration

[Neimhin]

@NeasaNi

• bat-mirialta sidebar beside the story composition page
• avoid double login

Mockup:

We want to integrate the bat-mirialta into the An Scéalaí story editor, e.g. when a user makes 3 mistakes with briathar neamhrialta we prompt the user to practice verbs with the bat.
Quick and dirty solution will be to use an iframe and force the user to login with an abair account to continue using the bat.
Longer term the UI should be integrated and should not require a second login.

[Neimhin]

Progress here:
phonlab-tcd/bat-mirialta#2