Create setters for loginText and logoutText to make LoginButton more …

…customizable (#543)

Summary:
I've found myself in situations where I have to take login/logout texts from an external source. Even though Facebook provides a lot of translations in project resources and also allow us to set these texts via xml attributes, I haven't found a solution for setting these texts programmatically.
Pull Request resolved: #543

Reviewed By: codytwinton

Differential Revision: D14408595

Pulled By: jingping2015

fbshipit-source-id: c640f0cb7f1c7fe2add8e8f2c0df775d9eefd44a

facebook-login/src/main/java/com/facebook/login/widget/LoginButton.java

@@ -241,6 +241,16 @@ public LoginButton(Context context, AttributeSet attrs, int defStyle) {
                 AnalyticsEvents.EVENT_LOGIN_BUTTON_DID_TAP);
     }
 
+    public void setLoginText(String loginText) {
+        this.loginText = loginText;
+        setButtonText();
+    }
+
+    public void setLogoutText(String logoutText) {
+        this.logoutText = logoutText;
+        setButtonText();
+    }
+
     /**
      * Sets the default audience to use when the user logs in.
      * This value is only useful when specifying publish permissions for the native