Rewrote the convoluted return statement of getContentFromGunAndIPFS into a linear code flow.

See merge request rysiekpl/libresilient!8

Implement integrity check plugin

Closes #20

See merge request rysiekpl/libresilient!7

simple integrity plugin

Closes #19

See merge request rysiekpl/libresilient!6

Subresource Integrity exposed to plugins from Service Worker

See merge request rysiekpl/libresilient!5

Docker shared runners used for tests

See merge request rysiekpl/libresilient!4

Improved plugin loading

See merge request rysiekpl/libresilient!3

service-worker: tests fixed for the new plugin loader, and a test added for using multiple instances of the same plugin (ref. #15)

service-worker: plugin loader rewritten, enabling using the same plugin multiple times (ref. #15); any-of: using the "uses" config field instead of old "plugins"