Added "Month to Date" Time Frame Option

Modified strings.xml to add "Month to Date" String (No translations
sorry)
Modified charts_menu.xml files to Add "Month to Date" Option
Modified Prefernces.java to add "MONTH_TO_DATE" to Timeframe enum
Modified BaseChartActivity.java to include "MONTH_TO_DATE" in
onCreateOptionsMenu() and onOptionsItemSelected(). Copied the
functionality of the other options
Modified ContentAdapter.java to include "MONTH_TO_DATE" to
getAdmobStats() and getStatsForApp(). Using
Calendar.getInstance().get(Calendar.DAY_OF_MONTH); to grab the day of
the month to set again the limit.