Use input text boxes to set custom range

When a user need to go back a while ago, it is cumbersome to click calendar buttons - it would be better to use input boxes. Currently the values of the input boxes are merely from calendar.

This commit allows a user to change the input boxes to set the range.

- do not change the input boxes when the cursor is over calendar date
- enable the input boxes when they or custom range option is clicked
- revert to old values when dates are invalid