makes enhancements to dmca system

[jessopb]

Visiting a content page shows an AssetBlocked component. Visiting a component page still attempts to fetch() the file in order to elicit the 451 error. I didn't want to send a 451 on document because document generally doesn't reload during normal navigation, and the document hangs on to the status throughout browsing. (This is also an issue for the 404). Visiting a Channel page, until we redo pagination, Blocked content shows a customized 451 channel preview. Blocklist is now in memory in a javascript Set() though I noticed no speed gains compared to local DB. Blocklist Endpoint is now a configurable siteConfig.json -> details -> blockListEndpoint : "" parameter. LBRY's blocklist is still the default configuration if blockListEndpoint is missing or null.

• three states of blockListEndpoint tested:
  • api-url
  • "" empty string
  • null => defaults to api-url

Blocklist Set() updates from database every 60 seconds, in preparation for periodic database updates in the future. Some extraneous .then()s in promise chains removed. See slack channel for test url.

[skhameneh]

When you're ready, merge to master, cut to staging, and have us (including @tzarebczan) test this.