[FIX] web: datetime value parsing without time

If the date format language was changed to invert month & day values (so, changed to the classic european format instead of the american format)
Then, when entering manually a datetime without the time (so just '01/02/2014' instead of '01/02/2014 00:00:00', the day and month were inverted (the datetime was set to 02/01/2014 instead of 01/02/2014) because the datetime entered did not exactly match the date + time pattern.

We therefore added a fallback case, to test to parse the value with the date pattern alone (without the time)