Timestamp method should use correct default <Day>

When you use the "Timestamp" method to set dates of files from their names you can omit the <Day> tag (because it is not part of the file name) and Advanced Renamer will substitute the last day of the month for it.
At least I conclude that from the error message
Invalid timestamp: '2016.11.31 18:11:14,0' is not a valid date and time
given in a tool tip windows for the error column of the respective file.
The year and month were correctly retrieved from the file name, and the time was correctly left as it was before.
But obviously Advanced Renamer took 31 as the (default) DAY value and then correctly concluded that the 31st of November should not exist.
It would be better if Advanced Renamer would
- choose a correct DAY value for the month
- would allow the user to choose a default DAY value, using e.g. a <Day=10> tag

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