Creates the app.R using the templates defined in inst/cheetah/*

Based on the configuration defined in config.yml the app.R code is created

create_shinyapp(params, target_file = "app.R", template_file = NULL)

Arguments

params	the params for creating app.R
target_file	(optional) default is app.R , you can change this
template_file	(optiona) this is an override.Function expect that you params$template_file is set in params when template_file is NULL