Make some way to refresh comic metadata

[josharian]

Temporary api glitches leading to missing comic data (such as happened with 1064) are currently cached permanently and irrevocably in the app. There should be some way, programmatic or manual, local or remote, to trigger silent redownloading/updating of comic metadata.

[josharian]

One simple suggestion is to have it triggered by image deletion, and to do an attempt at async replacement (so if it fails, the old data remains in place, and if it succeeds, it silently overwrites the old data).

[josharian]

This needs to autorefresh, it turns out. The transcripts lag, and we need to pick them up for better search and full accessibility.