Add choice of 7 days to settings for dynamic playlists (#616)

* Add choice of N days to settings for dynamic playlists (#3)

* Code review

app/src/main/java/com/kabouzeid/gramophone/util/CalendarUtil.java

@@ -29,6 +29,18 @@ public class CalendarUtil {
     }
 
     /**
+     * Returns the time elapsed so far last N days in milliseconds.
+     *
+     * @return Time elapsed since N days in milliseconds.
+     */
+    public long getElapsedDays(int numDays) {
+        long elapsed = getElapsedToday();
+        elapsed += numDays * MS_PER_DAY;
+
+        return elapsed;
+    }
+
+     /**
      * Returns the time elapsed so far this week in milliseconds.
      *
      * @return Time elapsed this week in milliseconds.

app/src/main/java/com/kabouzeid/gramophone/util/PreferenceUtil.java

@@ -290,6 +290,10 @@ public final class PreferenceUtil {
                 interval = calendarUtil.getElapsedWeek();
                 break;
 
+             case "past_seven_days":
+                interval = calendarUtil.getElapsedDays(7);
+                break;
+
             case "past_three_months":
                 interval = calendarUtil.getElapsedMonths(3);
                 break;