slight change to the text for the deleted and hidden item landing page.

fixed some grammar, and don't show 403 for hidden.
show doi as a link
stick with the capitalized resource name in landing page text

although downcasing it sounds more natural, it is complicated by the fact SOP needs to be capitalized.
Also, the resource name is treated as special noun.
We should review our use of capital or not, and update the locale if necessary to be consistent
some refactoring of the import of Doi module for active record

so that the model states if it supports_doi? to allow the types to be discovrabel and avoid hard-coded types in the Utils class. Also makes some of the code a bit cleaner. Removed from acts_as_asset, as currently not all assets support doi.
updated doi_locked_after to doi_time_locked_for

its a configuration flag to say that a DOI cannot be generated for an asset
until a particular period after it's creation time
fix to can_delete? based on the doi status

needed fixing after earlier refactoring, the module include order is important for
state_allows_delete? and must come after acts_as_authorized, or acts_as_asset
some code tidying and refactoring of datacite_doi lib
removed some duplicated code for doi generation

moved over to the model, and it can be generated doi can be got directly from the asset instance
a simple confirmation step before creating a DOI

it warns you that afterwards hiding or deleting the item will not be easy
test fixes