Language tag constraints added, ReferenceCardinality removed, example updated

[IMFTool]

<RFC5646SpokenLanguage> (Audio Virtual Track) and <RFC5646LanguageTagList> (Timed Text Virtual Track) constraints added, ReferenceCardinality removed.

Note 1: RFC5646SpokenLanguage is mandatory per ST 2067-2, if the soundfield group is associated with a primary spoken language.

Therefore, a simple element for specifying the expected language tag has been implemented.

Note 2: RFC5646LanguageTagList is optional for Timed Text files. Therefore, a (mutually exclusive) choice between two constraints has been implemented, examples given below:

                    <RFC5646LanguageTagListConstraints>
                        <!-- Option 1: Explicitely specify a list of language tags to be present in RFC5646LanguageTagList -->
                        <RFC5646LanguageTagList>de-DE,en,es-419</RFC5646LanguageTagList>
                    </RFC5646LanguageTagListConstraints>

or

                    <RFC5646LanguageTagListConstraints>
                        <!-- Option 2: SpecifyRFC5646LanguageTagList has to be present  -->
                        <RFC5646LanguageTagListPresent>true</RFC5646LanguageTagListPresent>
                    </RFC5646LanguageTagListConstraints>

Note 3: The pattern allows for language tags consisting of a language (e.g. "de") or a language plus a region, e.g. ("es-419")

Please comment, in case you have conflicting or additional requirements!