added on method
Using `options.elementsContainer` to calculate ID

Since the container for toolbar and anchor input can be changed to be 
other than `document.body`, in some cases, querying for the number of
`.medium-editor-toolbar` from `document` will not work. This made all
editor instances to have the same ID of 1.

Shadow DOM is an example in which, if `options.elementsContainer` is
set to an element inside it, it will not be available in the Light DOM to
query.

This updated to use `options.elementsContainer` to query for number of
`.medium-editor-toolbar` elements.
Fixed style to pass jslint
passing tests
passing tests
Merge branch 'tear-down'
merged davi's changes
added test for teardown
Merge pull request #329 from botverse/master

Removing events during deactivate
Merge pull request #328 from sntran/patch-1

Using `options.elementsContainer` to calculate ID
Updates autoprefixer
Updates dist files
1.9.13