R1:42b81a80900d

Move build statuses to a constants class

Summary: No functional changes here, just lifting this out to make room for activities, heeding lint warnings along the way.

Test Plan:
before:
```lang=bash
$ grep -Rn "HarbormasterBuild::" *
src/applications/harbormaster/storage/HarbormasterBuildable.php:169: $build = HarbormasterBuild::initializeNewBuild($viewer)
src/applications/harbormaster/storage/HarbormasterBuildable.php:173: ->setBuildStatus(HarbormasterBuild::STATUS_PENDING)…