Add unique ID to <bond> element to force re-render after bond definition

[fonsp]

This fixes the following situation, where a bond is placed inside a DivElement:

Schermopname.2022-01-18.om.13.04.00.mov

Because the HTML contents of the bond (<bond def=x><input type=range></bond>) are exactly the same, Pluto's frontend will do a partial re-render of the third cell, skipping the re-render of the sliders, since those are unchanged. This means that the bond value is not set.

This is a problem, because re-running a @bond expression will always remove the old bound value from Julia scope.

This PR will guarantee that re-running @bond will cause the HTML element to re-render, by including a random string (generated when the Bond is created) in the HTML output.

[github-actions]

Try this Pull Request!

Open Julia and type:

julia> import Pkg
julia> Pkg.activate(temp=true)
julia> Pkg.add(url="https://github.com/fonsp/Pluto.jl", rev="bond-unique-id")
julia> using Pluto