The extension version used throughout the wallet is now normalized to a
SemVer-compliant version that matches the version used in
`package.json`. We use this version for display on the "About" page,
and we attach it to all error reports and metric events, so it's
important that we format it consistently so that we can correlate
events on the same version across different browsers.
This normalization step is necessary because Firefox and Chrome both
have different requirements for the extension version, and neither is
SemVer-compliant.
