ISSUE #36: hour format character mismatch between gwt DateTimeFormat and...

... bootstrap DateTimePicker

added replacement of "h" to "H" and "H" to "h". This could not be done with ```.replaceAll```, as the second call would have reverted the change of the first.
Now we iterate over the characters of the string and look them up in the map of discrepancies. Therefore it's safe to "toggle" case, as each character is only processed once, plus it's safer now, as the execution order of ```replaceAll```s does not matter anymore.