Initial commit for allowing other themes (e.g. Bulma, Material) in ob…

[bcaessens]

…serve_helpers.R

added useTheme argument to observe_helpers added example for bulmaApp.R added Bulma.md helper file with formula (not working)

[bcaessens]

I hope I did this right, I am always somehow confused using git, Rstudio git and github....

[cwthom]

Thanks @bcaessens - just a heads up this is going to take me a little while to get to, but I will try soon!