Optionally match emails against *either* whitelist or domains when both are provided (#106)

The previous behaviour would ignore domains if the whitelist parameter was provided, however if both parameters are provided then matching either is more likely the intent.

internal/config_test.go

@@ -34,6 +34,7 @@ func TestConfigDefaults(t *testing.T) {
 	assert.Len(c.Domains, 0)
 	assert.Equal(time.Second*time.Duration(43200), c.Lifetime)
 	assert.Equal("", c.LogoutRedirect)
+	assert.False(c.MatchWhitelistOrDomain)
 	assert.Equal("/_oauth", c.Path)
 	assert.Len(c.Whitelist, 0)