Get element attributes dict without accessing private parameter _attributes

[flyte]

Is there a reason _attributes should not be publicly accessible? It's useful for me to get this out as a dict. I guess there's a reason to not allow external changes to _attributes, hence the copy().

[coveralls]

Coverage increased (+0.9%) to 36.19% when pulling 820ef249cfb6c07fdb0996e63cbc0f49b2f80573 on flyte:patch-1 into 2119763f721b23588b6223f28264843f6fc9f750 on stchris:master.