Fix for date picker (and maybe more)

[andykillen]

Perhaps customizer has been updated in the last 4 years since this set was made. There needs to be added

<?php echo $this->get_link() ?>

to each of the input html so that wordpress knows there is a change and the save button updates, and of course the data gets saved

example for date picker

<label>           
          <span class="customize-date-picker-control"><?php echo esc_html( $this->label ); ?></span>
          <input <?php echo $this->get_link() ?>  type="date" id="<?php echo $this->id; ?>" name="<?php echo $this->id; ?>" value="<?php echo $this->value(); ?>" class="startcamp_datepicker" />                    
        </label>

I'm not making a pull request as it seems to me clear that this is a dead project. I'm leaving this here so others can find out the fix.