Upgrade dropzone to 5.5.0

[Robert Lyon]

Upgrade the plugin to new major version

[Mahara Bot (dev-mahara)]

Patch for "master" branch: https://reviews.mahara.org/9411

[Steven (stevens-q)]

Environment tested: Master
Browser tested: Chrome

PRECONDITIONS:
------------------------
1) null

TEST STEPS:
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1) User log in as Site admin
2) Browse to Main menu > Create > Files
3) User drag files from your local folders and drop them in the "Drop files here to upload" section of the page
4) Verify that no errors are encountered and files are uploaded ✔

Catalyst QA Approved ✔

[Mahara Bot (dev-mahara)]

Reviewed: https://reviews.mahara.org/9411
Committed: https://git.mahara.org/mahara/mahara/commit/4f8f034ad4d258929874ac60935de1ad984c495a
Submitter: Cecilia Vela Gurovic (<email address hidden>)
Branch: master

commit 4f8f034ad4d258929874ac60935de1ad984c495a
Author: Robert Lyon <email address hidden>
Date: Thu Jan 10 11:08:40 2019 +1300

Bug 1811153: Upgrading dropzone to 5.5.0

behatnotneeded

Change-Id: I11b6f2a6f057e3d71c38065a317161c78f2b3999
Signed-off-by: Robert Lyon <email address hidden>