WIP: show custom relics as alts

[xpdota]

Not substantially started yet, just a placeholder PR.

There are two ways to go with this:

1. The full option - look at valid combinations of relic stats and accurately display relics as alts for any item which might be replaceable by a relic. This is harder but more complete.
2. The easy option - treat relics as interchangeable with other relics only. Look at the relic stat models plus stat caps.
3. The easiest option - treat relics as interchangeable within the same relic "type" (i.e. full custom vs choose from fixed options).

Optino 1 requires a more substantial refactor because it would need to consider the item "as equipped" rather than "as it exists in the data files" - for example, there may or may not be a valid non-relic alternative to a relic based on the stats chosen on the relic.