A11y

I think this should fix some keyboard accessibility issues with dialogs:

1) Focus returns to the original button/link when you close a dialog.
2) Tabbing cycles through the content of a dialog until you close it.
3) Added role="dialog" and some ARIA attributes.

Tested with a local copy of Op. War Diary and it seemed to work. Someone else should probably have a look before it gets merged into master.