added SeparatePluginInstances SeparateTypeInstances parameters to graphite plugin to do more flexible naming scheme

With  SeparateInstances parameter set to true

The collectd-naming schema:

```
host "/" plugin ["-" plugin instance] "/" type ["-" type instance]
```

becomes ( once sended to graphite)

```
host / plugin / plugin instance / type / type instance
```

now we can choose separate plugin and type instance separately ( or together with old parameter)

if SeparatePluginInstances=true

```
host / plugin / plugin instance / type - type instance
```
will be send to graphite 

if SeparateTypeInstances= true

```
host / plugin - plugin instance / type / type instance
```
will be send.