Mesh argument ranges

[simon-smart88]

@timcdlucas

I realised I didn't have all the mesh parameters included, so have added concave, convex and resolution here: 77e8152

I don't know what sensible ranges for them are though so would be good to discuss at some point. This is what I've used so far:

    sliderInput(ns("convex"), "Convex", min = -0.05, max = 0.05, value = -0.01, step = 0.01),
    sliderInput(ns("concave"), "Concave", min = -1, max = 1, value = -0.5, step = 0.1),
    sliderInput(ns("resolution"), "Resolution", min = 10, max = 1000, value = 300, step = 10),

I also wondered whether we should have the option to make multiple meshes and pick one to use?