Starting the rollback of flag categories.

I left in the old FlagRegisterer constructor.
I also left in 'categories' in CommandLineFlagInfo for now,
though I never use it.  I doubt anyone else does either, but I
want to minimize the number of ways this rollback can break
the build.  I will remove it in a subsequent CL.

DELTA=121  (28 added, 55 deleted, 38 changed)

Revision created by MOE tool push_codebase.

git-svn-id: 6586e3c6-dcc4-952a-343f-ff74eb82781d
6 files changed