config: add wiki links

main wiki link included with "about" and "user profiles". Sections with
a relevant page have a linked button next to their title when clicked.
Behaviour added by the "wiki_link" field in the "meta" section of a
config "section".

models.go

@@ -214,6 +214,7 @@ type meta struct {
 	Advanced     bool   `json:"advanced,omitempty"`
 	DependsTrue  string `json:"depends_true,omitempty"`
 	DependsFalse string `json:"depends_false,omitempty"`
+	WikiLink     string `json:"wiki_link,omitempty"`
 }
 
 type setting struct {