add prior explorer - tiny shiny app?

[aappling-usgs]

definitely a wish list item, not immediate:

write a function that accepts a specs list of priors (could even use manipulate or Shiny to return an edited list), e.g.:

  GPP_daily_mu             10                                                                            
  GPP_daily_sigma          10                                                                            
  ER_daily_mu              -10                                                                           
  ER_daily_sigma           10                                                                            
  K600_daily_mu_mu         30                                                                            
  K600_daily_mu_sigma      30                                                                            
  K600_daily_sigma_shape   1                                                                             
  K600_daily_sigma_rate    0.5                                                                           
  err_obs_iid_sigma_shape  1                                                                             
  err_obs_iid_sigma_rate   10                                                                            
  err_proc_iid_sigma_shape 1                                                                             
  err_proc_iid_sigma_rate  100  

and visualizes the priors distributions indicates by that specs list.

i often forget how and/or don't bother to do this. would be nice to see a set of plots like the following but prettier, informatively labeled, and showing all of the relevant distributions (one plot for GPP_daily, one for K600_daily_mu, etc.)

x <- seq(0,5,by=0.1)
plot(x, dgamma(x, shape=1, rate=0.5), type='l', ylim=c(0,1), ylab='dgamma')
lines(x, dgamma(x, shape=1, rate=10), col='blue')
lines(x, dgamma(x, shape=1, rate=100), col='red')