Additional changes for WG LC preparation

[italobusi]

• Updated XPath in the leafref for supported application codes and supported organizational modes: fix #95
• Resolved yanglint warnings: fix #91
• Updated data types for max-diff-group-delay, min-Q-factor, available-baud-rate data types: fix #94
• Added new identities for wavelength assignment: fix #92
• Cleaned up the OTU type definitions: fix #21
• Moved authors to contributors list: fix #90

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Co-authored-by: sergio belotti sergio.belotti@nokia.com