Config unification

Replace Candlepin's Config class with Configuration from common. No more ```new Config()``` in mainline code, rely on injection of Configuration from Guice.

TEST
---------
Simply do what you normally do to use Candlepin.

NOTE: I did not update Gutterball.
Having this be static means I have to remove it from the ```Configuration``` interface. Which I guess is fine, but it does feel weird. 

Also, what does returning the implementation class buy us?  Here's what we do with it today. I'm trying to get a mental picture of what it would look like if we change it to what you suggest:

```
    protected Configuration readConfiguration(ServletContext context)
        throws ConfigurationException {

        // Use StandardCharsets.UTF_8 when we move to Java 7
        Charset utf8 = Charset.forName("UTF-8");
        PropertiesFileConfiguration systemConfig = new PropertiesFileConfiguration();
        systemConfig.setEncoding(utf8);
        File configFile = new File(ConfigProperties.DEFAULT_CONFIG_FILE);

        if (configFile.canRead()) {
            log.debug("Loading system configuration");
            // First, read the system configuration
            systemConfig.load(configFile);
            log.debug("System configuration: " + systemConfig);
        }

        // load the defaults
        MapConfiguration defaults = new MapConfiguration(
            ConfigProperties.DEFAULT_PROPERTIES);

        log.debug("Loading default configuration values");

        // merge the defaults with the system configuration. ORDER MATTERS.
        // system config must be read FIRST otherwise settings won't be applied.

        // merge does NOT affect systemConfig, it just returns a new object
        // not sure I like that.
        return systemConfig.merge(defaults);
    }
```

This would then look like
```
 PropertiesFileConfiguration systemConfig = new PropertiesFileConfiguration();
...
       systemConfig.load(configFile);
...
        MapConfiguration defaults = new MapConfiguration(
            ConfigProperties.DEFAULT_PROPERTIES);
...
    return PropertiesFileConfiguration.merge(systemConfig, defaults); 
```