Adding onClick-Event for calendar space without items

[ChristianPetersen]

I have used this scheduler for an availability calendar for holiday rentals.
Therefore I needed the ability to click on whitespace in order to start a function. After some tweaking in the CSS, I needed the table-cells for the calendar to carry information about their row and column.
The now carry some attributes. If anyone should need this, please look at https://www.more-bookings.com and send me a note.
I have no idea how to get my version into github with pull requests, but I am very willing to learn.

Christian