Add Opinion entity and add opinions on article

src/main/kotlin/fr/dcproject/entity/Opinionable.kt

@@ -0,0 +1,9 @@
+package fr.dcproject.entity
+
+interface Opinionable {
+    val opinions: MutableMap<String, Int>
+}
+
+class OpinionableImp : Opinionable {
+    override val opinions: MutableMap<String, Int> = mutableMapOf()
+}