Allow multiple signature regexes & add Dutch send from my iPhone sig…

[MarkKremer]

In this PR:

1. Use an array of signature regexes instead of a single one. This is similar to how it works for quote headers.
2. Added the Dutch "sent from my iPhone" signature.

Breaking changes:

1. setQuoteHeadersRegex and getQuoteHeadersRegex use arrays instead of strings. Applications using these methods must be updated.

Related to https://github.com/willdurand/EmailReplyParser/issues/69 but I went in a different direction.