Fixed the bug that input fields with name 'action' override the form.action attribute.

Fixes #252
Added a Dropzone.confirm function.

#changelog Closes #255
Added a maxFiles option which provides the functionality to limit the Dropzone to a maximum number of handled files.

#changelog, closes #28
The dropzone element gets a dz-max-files-reached class now when maxFiles has been reached or exceeded.

#changelog
Added download files.
Upgrading version to 3.7.0 (Bug fixes, added the Dropzone.confirm method and Dropzone.maxFiles(!).)
Upgrading version to 3.7.1-dev