add pluginBundle support

A plugnBundle is meta plugin that has a set of dependent plugins
to enable.  This commit includes a plugin.json for a default
"core" bundle that enables all of the shipped panels and datasources.

pkg/api/datasources.go

@@ -115,8 +115,11 @@ func UpdateDataSource(c *middleware.Context, cmd m.UpdateDataSourceCommand) {
 
 func GetDataSourcePlugins(c *middleware.Context) {
 	dsList := make(map[string]interface{})
+	//TODO(awoods): query DB for orgPlugins
+	orgPlugins := map[string]m.PluginBundle{}
+	enabledPlugins := plugins.GetEnabledPlugins(orgPlugins)
 
-	for key, value := range plugins.DataSources {
+	for key, value := range enabledPlugins.DataSourcePlugins {
 		if !value.BuiltIn {
 			dsList[key] = value
 		}