Move setup of Rebase's ChangeJson to constructor

Rebase is now a singleton.  The ChangeJson it holds is private to
itself, but is also effectively a singleton.  Configure its option
list once at creation time.

Change-Id: I6c2851f5b37c75596ecc076cc1bbf09805afdde4
Remove @Singleton from PutIncludedGroup

This object is manually constructed with a unique value per instance
in the id field.  It cannot be a singleton.

Change-Id: I314ef34185523d96e6f1e9ae809fde36b5eedc2f
Mark ApprovalCopier, ApprovalsUtil and LabelNormalizer as singleton

These have no per-request state and are held by several REST API views
that are themselves singletons.  Instead of making one copy per REST
view, make these singletons for the server.

Change-Id: I2f343d29c4bed8a862b3794323916ca46b8b1f99