modules: camera: Metadata refactor

Add* functions const to protect data being added.
Initiailze metadata object from a camera_metadata_t.
Remove template-specific constructor.
Add convenience "add1" method to abvoid stack-allocated data.
Construct templates manually (in ExampleCamera) from base.

Change-Id: I3201f61e9d32841ea7a769d69242b40d8727c02e
6 files changed