Bug956436 new release type update channel

Prior to this commit, four different terms for similar things were in
use:
    * build_type
    * release_type
    * release_channel
    * build_channel

We're redefining these terms to just two:

    * build_type: Socorro-defined list of build types, manually configured
    * update_channel: any build/release information passed through
      breakpad by vendors. Can be *anything* and is unfiltered

Unsupported uses of these terms have been marked as DEPRECATED.

Future PRs will include changes to code an stored procedures to use
the new columns. When that work concludes, the DEPRECATED columns can be
removed.