userFractionGauge: Server-side code for generic KPI gauge.
In IskanderBlue/morseldash: Makes Building Dashboards for Morsel Easier

Server-side code for generic KPI gauge. Uses dplyr:: functions to figure out what percentage of users were previous aware of the product.

userFractionGauge(input, output, session, fdat, pcol, threshold,
  pos_options = "Yes", symbol = "%", title = "Indicator",
  minRange = 0, maxRange = 100, reversed_values = FALSE,
  reversed_colors = FALSE)

`input`	Required for shiny modules' server functions.
`output`	Required for shiny modules' server functions.
`session`	Required for shiny modules' server functions.
`fdat`	dataframe, filtered by demographic variables and product.
`pcol`	numeric, the number of fdat's column containing the question of interest.
`threshold`	numeric, the cutoff between positive and negative colors.
`pos_options`	vector, all the strings in fdat[[pcol]] that are considered 'good' responses.
`symbol`	string, indicates unit of numeric output (eg. "%").
`title`	string, title for gauge.
`minRange`	numeric, minimum value for gauge.
`maxRange`	numeric, maximum value for gauge.
`reversed_values`	logical, indicates whether to flip values (e.g. gauge_value <- maxRange - gauge_value )
`reversed_colors`	logical, indicates whether low values are 'good'/green and high values are 'bad'/red or not.