fix(datepicker): Multiple datepicker fixes

The IE fix needs the following CSS lines in the angular-strap.css:

.datepicker-day-view {
  width: calc(100%/7);
  /*250px-75px = 175px*/
  height: calc(175px/5);
}
.datepicker-month-year-view {
  width: calc(100%/4);
  /*250px-50px = 200px*/
  height: calc(200px/3);
}

I have extracted the values from the directive. For some reasons, IE does not refresh scope.width and scope.height when you change the view mode. So if you display the day mode with 7 columns of 14% each, the month view will display only 4 columns with the same 14%. About 2/3 of the popup space.

The code has been tested on Chrome, Safari, FF, IE9 & IE 11 and somes devices.