Move styles for button, checkbox and pulldown

[#41475421]
Add a new structure for keeping custom pairwise LJ properties

[#41834627]
Add tests of custom pairwise LJ properties collection object

[#41834627]
Add pairwiseLJProperties to metadata

[#41834627]
Support Pairwise LJ Properties in MD2D engine

[#41834627]
Support Pairwise LJ Properties in MD2D modeler

[#41834627]
Expose setPairwiseLJProperties function in Scripting API

[#41834627]
Add a new interactive and model for testing custom LJ properties

[#41834627]

Note that work is still in progress, so interactive isn't finished.
However it's possible to test custom LJ properties using the browser
console.