Merge branch '236-use-ed25519' into 'master'

.../org/briarproject/bramble/api/crypto/CryptoComponent.java

.../org/briarproject/bramble/api/crypto/CryptoConstants.java

...in/java/org/briarproject/bramble/api/identity/Author.java

...rg/briarproject/bramble/api/identity/AuthorConstants.java

.../org/briarproject/bramble/crypto/CryptoComponentImpl.java

...n/java/org/briarproject/bramble/crypto/SignatureImpl.java

...a/org/briarproject/bramble/crypto/EcdsaSignatureTest.java

...java/org/briarproject/bramble/crypto/EdSignatureTest.java

...riarproject/bramble/crypto/KeyEncodingAndParsingTest.java

...riarproject/briar/introduction/IntroductionValidator.java

...riarproject/briar/introduction/IntroduceeManagerTest.java

...oject/briar/introduction/IntroductionIntegrationTest.java

...project/briar/introduction/IntroductionValidatorTest.java