Properly store certificate exceptions in Java viewer

Properly store certificate exceptions in Java viewer

Like the native viewer, the Java viewer didn't store certificate
exceptions properly. Whilst not as bad as the native viewer, it still
failed to check that a stored certificate wouldn't be maliciously used
for another server. In practice this can in most cases be used to
impersonate another server.

Handle this like the native viewer by storing exceptions for a specific
hostname/certificate combination.

(cherry picked from commit f029745f63ac7d22fb91639b2cb5b3ab56134d6e)