Add an option to set the max number of rows shown in the output table for keyboard event viewer

[garykac]

From @AricMonary in w3c/uievents#364

Output table is hard-coded for 100 rows. There have been times where I would like to view more than 100 keyboard events at a time using the keyboard event viewer.

Add an input field to the options to set the max number of rows shown.

See pull request: w3c/uievents#364 (reference)