Show campaigns (#2113)

* Show campaigns
* Added a ui util class SwipableCardView which passes the onSwipe event to its children
* NearbyCardView & CampaignView extend SwipableCardView
* Fetch campaigns in ContributionsFragment
* Added an option to enable disable campaign in Settings/Preferences

* synced strings with master

* removed duplicate initialsation of CampaignPresenter

app/src/main/java/fr/free/nrw/commons/BasePresenter.java

@@ -0,0 +1,16 @@
+package fr.free.nrw.commons;
+
+/**
+ * Base presenter, enforcing contracts to atach and detach view
+ */
+public interface BasePresenter {
+    /**
+     * Until a view is attached, it is open to listen events from the presenter
+     */
+    void onAttachView(MvpView view);
+
+    /**
+     * Detaching a view makes sure that the view no more receives events from the presenter
+     */
+    void onDetachView();
+}