Fix EscKeyDownHandler bug in Container when closable is false

[kevinzwhuang]

Description:
There is a bug in lock when Container is set to container: "name" and the ESC button is pressed, this error occurs:

Uncaught TypeError: closeHandler is not a function - container.js:119
  handleClose @ container.js:119
  handleEsc @ container.js:128
  EscKeyDownHandler.handler @ container.js:54

The lock has the container UI option set to true, which should cause closable to change to false as well, as per the #Customization section in the docs - so this behavior should not be expected, since the lock is still expecting a function to handle close.

Changes Proposed:

• Add condition to only mount Container component with EscKeyDownHandler to this.escKeydown when a closeHandler prop exists.
• Add condition to only release this.escKeydown if this.escKeydown exists on Container unmount.

The changes above should prevent any further errors from the container attempting to close, when it should not be able to.

[kevinzwhuang]

Thoughts on this bug fix @cristiandouce @hzalaz?

[cristiandouce]

@kevinzwh thanks for the PR! I'll take a look at it tomorrow and merge.

Would you mind squashing your commits?

Thanks again!

[kevinzwhuang]

Commits are squashed, thanks @cristiandouce