Make Attachment immutable

[philipphofmann]

Attachment has a setter for contentType. We can remove the setter and pass the param to the constructors instead. This means we need to add two constructors:

public Attachment(final @NotNull String pathname, final @NotNull String filename, final @NotNull String contentType) {
  // ...
}

public Attachment(final @NotNull byte[] bytes, final @NotNull String filename, final @NotNull String contentType) {
  // ...
}

With this, we achieve immutability for Attachments.

[philipphofmann]

@bruno-garcia, @marandaneto, @maciejwalkowiak any objections to this change?

[marandaneto]

no objections, just out of curiosity, what was the motivation to be a setter before? if none, even better :D

[philipphofmann]

I think I thought having to pass 3 parameters to a constructor is maybe a bit too much and we were not really sure back then if we even need content type. I think 3 parameters are fine. I can't remember what drove me back then.