Make github a multisource widget

Note, that this is a backwards incompatible change

Previous config:

```
repositories:
  wtf: "wtfutil"
```

New Config:

```
repositories:
- "wtfutil/wtf"
```

modules/github/settings.go

@@ -5,6 +5,7 @@ import (
 
 	"github.com/olebedev/config"
 	"github.com/wtfutil/wtf/cfg"
+	"github.com/wtfutil/wtf/wtf"
 )
 
 const defaultTitle = "GitHub"
@@ -15,7 +16,7 @@ type Settings struct {
 	apiKey       string
 	baseURL      string
 	enableStatus bool
-	repositories map[string]interface{}
+	repositories []string
 	uploadURL    string
 	username     string
 }
@@ -28,7 +29,7 @@ func NewSettingsFromYAML(name string, ymlConfig *config.Config, globalConfig *co
 		apiKey:       ymlConfig.UString("apiKey", os.Getenv("WTF_GITHUB_TOKEN")),
 		baseURL:      ymlConfig.UString("baseURL", os.Getenv("WTF_GITHUB_BASE_URL")),
 		enableStatus: ymlConfig.UBool("enableStatus", false),
-		repositories: ymlConfig.UMap("repositories"),
+		repositories: wtf.ToStrs(ymlConfig.UList("repositories")),
 		uploadURL:    ymlConfig.UString("uploadURL", os.Getenv("WTF_GITHUB_UPLOAD_URL")),
 		username:     ymlConfig.UString("username"),
 	}