[analyzer] Overhaul of checker registration in preparation for basic plugin support. Removes support for checker groups (we can add them back in later if we decide they are still useful), and -analyzer-checker-help output is a little worse for the time being (no packages).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@137758 91177308-0d34-0410-b5e6-96231b3b80d8
19 files changed