Update device management with newtmgr page and add it to OS User Guide.
Newt Manager
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+.. toctree::
+ :maxdepth: 1
+
+ Using the OIC Framework <oicmgr>
+ Customizing Newt Manager Usage with mgmt <customize_newtmgr>
+
+
Newt Manager is the protocol that enables your Mynewt application to
communicate remotely with your device running the Mynewt OS in order to
configure, manage, conduct maintenance, and monitor it. The core device
