Fix #4: Add "lock" option to disable ESC closing
Clean up alert options handling
Clean up confirm options handling
Clean up prompt options handling
Fix #5: Click backdrop to dismiss

A truthy "lock" option passed to .dialog disables backdrop
click-to-dismiss and does not show the close button in the title.
Fix typo
Alerts should be "locked" by default
Make sure promise is rejected if modal closes
v0.2.4