A merged index that failed to load made mergeIndex throw, and the
failed instance stayed in the list, so search stopped working for
every index. Indexes passed with `optional: true` are now dropped
with a warning when they fail to load, and search runs over the
indexes that did load.
Fixes#887
Relative images were resolved against the page URL, but only the
pathname was kept, so with a baseUrl on another domain the image
still loaded from the search site. Keep the origin when the page URL
has one, in the Component UI's resolveUrl filter and in both Default
UI result templates. result_with_subs.svelte didn't resolve images at
all before.
Fixes#573
dualfroz