Move -config to a sample file, to avoid accidental overwrites upon upgrade

Signed-off-by: Andrew Phelps <andrew@phel.ps>
Remove _EMBEDLY_API_ENDPOINT constant, set default to 'embed' unless otherwise specified

Signed-off-by: Andrew Phelps <andrew@phel.ps>
Add blank -overrides file

Signed-off-by: Andrew Phelps <andrew@phel.ps>
Add PHP sanity check and Twitter credentials verification on startup

Signed-off-by: Andrew Phelps <andrew@phel.ps>