Minor improvements

[Lucas-C]

This patch adds the following features :

• numeric values for the inputs
• a button to hide the background image
• a button to join the dots with lines
• the ability to customize the dots indices (labels) with a custom function
• the ability to filter the dots included with a custom function

[Lucas-C]

A preview of the result can be found there: https://lucas-c.github.io/Connect-The-Dots-Generator/

[JEFworks]

Great features! Thanks Lucas!

[Lucas-C]

My pleasure ;)