Add non-stupid-digest-assets dependency

This is a transitionary measure that allows us to precompile certain
assets without a digest. The README provides an explanation of the use
cases for which this is needed:
https://github.com/alexspeller/non-stupid-digest-assets/blob/master/README.md#but-shouldnt-i-always-use-the-rails-asset-helpers-anyway

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Signed-off-by: Alex Coles <alex@alexbcoles.com>
Configure non-stupid-digest-assets whitelist

Bug # 8228

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Signed-off-by: Alex Coles <alex@alexbcoles.com>
Merge pull request #1379 from opf/fix/non-digest-assets