simplify how features are sorted into "other" category

[tyrasd]

addresses #9065:

• boundaries also includes all ways that are a member of a boundary relation
• ways that don't match any non-"other" category inherit the categories of all their parent relations
• other includes only the remaining tagged ways that don't match any other category

todos:

• handle case where feature is member of one relation (e.g. type=route) which does not match any category by itself
• test extensively
• add unit test for boundary ways
• add unit test for other category