Only "load" a theme when it is explicitly requested by the user. #1105
Previously, all installed themes were "loaded" each time the CLI
Previously, all installed themes were "loaded" each time the CLI was run. Now, only the names are obtained unless the user explicitly requests a theme by name (in user config for via command line option). A broken third party theme can no longer "break" a project in which is is not being used. Fixes #1104.