Require progress-reporters in spec_helper
Report a warning instead of an error in AddOrUpdateTranslationCommand

No need to report errors since PhraseNotFound errors are fairly
commonplace (and not fatal).
Pull out filtering methods from SnapshotFactory into their own module (SnapshotFilterable)
Introduce skeleton HeadSnapshotFactory

Should grab a “snapshot” of the current HEADs and ignore merges. In
other words, if the current tip of my_branch is a merge commit,
HeadSnapshot factory should search for the next child commit that is
NOT a merge and return that instead. This is consistent with how the
rest of Rosette works, i.e. always ignoring merge commits.