Migrate from nextcloud constants to attributes and subscribes (#32)

assets/dbp-official-signature-pdf-upload.metadata.json

assets/dbp-qualified-signature-pdf-upload.metadata.json

assets/dbp-signature-verification-full.metadata.json

assets/dbp-signature.html.ejs

rollup.config.js

src/dbp-official-signature-pdf-upload.js

src/dbp-qualified-signature-pdf-upload.js

src/dbp-signature-verification-full.js

vendor/toolkit