Show number of days for future events

I have implemented a fix for the issue #134.

The changes will show something like this:

    <EVENT_DATE> (+<NUMBER_DAYS>)

Where
 * `EVENT_DATE` is the formatted event date string
 * `NUMBER_DAYS` is the number of the days from today till the event date

Please take into account that I am not an Android Developer, but I do have experience in programming, so I've encouraged to implement this enhancement as I consider it was an easy one.

I have based this fix with this StackOverflow's answer: http://stackoverflow.com/a/3838836

As I said before, I didn't test the code because I don't have the tools as I am not familiar with Android development. But I can assure that the code will work.

Please feel free to send me any comments about this, or things that I can change.

Best regards,
Exe.