add taxonomies awereness to foreman_openscap
Fix a ISE on Postgresql

When approched /compliance/scap_contents/new with an organization
selected.

Addressing:
Operation FAILED: PGError: ERROR:  column reference "id" is ambiguous
LINE 1: SELECT id FROM "taxonomies" INNER JOIN "taxable_taxonomies" ...
               ^
: SELECT id FROM "taxonomies" INNER JOIN "taxable_taxonomies"
	ON "taxable_taxonomies"."taxonomy_id" = "taxonomies"."id"
	WHERE "taxonomies"."type" IN ('Location')
		AND "taxable_taxonomies"."taxable_type" = 'Scaptimony::ScapContent'
		AND "taxable_taxonomies"."taxable_id" IS NULL
	ORDER BY title
Fix policy#show after applying Authorizable.
Revert small part of #30.

I am not sure why it was needed. It seems to be working well without it.
Do not double define accessible attributes

These are already defined in SCAPtimony.
Remove overabundant lambda statement.

Addressing Rubocop suggestion:
C: default_scope expects a block as its sole argument.