js: Tests and improvements for openpgp mode

• Added openpgp - Mode tests to the browsertest Extension. These tests require openpgp, which should not be a hard dependency for the main project. Packing openpgpjs into the extension is still TODO

• Fixes:
  • openpgp mode API now correctly handles parameters as an object, similar to openpgpjs
  • proper check and parsing of openpgpjs Message Objects