Fixes T2383. Allows setup checks to be run from the CLI with ./bin/config check. The general idea is to split the PhabricatorSetupCheck::executeChecks method into three smaller components:
- PhabricatorSetupCheck::executeCommandLineChecks is used for running setup checks which are specific to the command line. We don't really have any of these, but this diff makes it possible for us to add these types of checks.
- PhabricatorSetupCheck::executeWebChecks is used for running setup checks which only make sense in a web context.
- PhabricatorSetupCheck::executeCommonChecks is used to execute common checks shared between the command-line and web.