Use global cache passed through corestore if available

[HDegroote]

Relies on https://github.com/holepunchto/hypercore/pull/535 and https://github.com/holepunchto/corestore/pull/94 (so draft PR)

Exposes the globalCache on its autocore sessions, if the corestore it was passed exposes it. This makes them compatible with the hypercore (with the linked PR). In particular, views generated from this autobase will use the globalCache (assuming hyperbee PR https://github.com/holepunchto/hyperbee/pull/161 is used).

This makes the maxCacheSize opt redundant, so I removed it. Technically this is a breaking change, but it was an unofficial option anyway (and no harm done if it's still passed in, it's just ignored).