Rename account to identity.

...va/org/briarproject/bramble/api/db/DatabaseComponent.java

.../java/org/briarproject/bramble/api/identity/Identity.java

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

...rc/test/java/org/briarproject/bramble/test/TestUtils.java

.../org/briarproject/bramble/account/AccountManagerImpl.java

...e/src/main/java/org/briarproject/bramble/db/Database.java

...va/org/briarproject/bramble/db/DatabaseComponentImpl.java

...c/main/java/org/briarproject/bramble/db/JdbcDatabase.java

...rg/briarproject/bramble/identity/IdentityManagerImpl.java

.../briarproject/bramble/account/AccountManagerImplTest.java

...rg/briarproject/bramble/db/DatabaseComponentImplTest.java

.../org/briarproject/bramble/db/DatabasePerformanceTest.java

...st/java/org/briarproject/bramble/db/JdbcDatabaseTest.java

...riarproject/bramble/identity/IdentityManagerImplTest.java

...g/briarproject/briar/feed/FeedManagerIntegrationTest.java

...ject/briar/messaging/SimplexMessagingIntegrationTest.java

...ava/org/briarproject/briar/test/BriarIntegrationTest.java