`getSupportedChartTypes()` should assess ds.cohort{addCharts{},hideCharts{}} and replace allowedChartTypes[]

[xzhou82]

getSupportedChartTypes() does two things:

1. compute chart types that can work for a ds, based on term type and data type availability. e.g. if survival term is present, allow survival chart. this computing only generate common chart types.
2. return allowed chart types per subcohort. mass client will show chart buttons solely based on this
3. optionally, apply ds overrides from a new structure below. addCharts will add things, hideCharts will hide things. this is a better design than allowedChartTypes[] that does two things and lead to excessive config on datasets

cohort {
  addCharts: {
     bySubcohort: {
       <cohort1>: [ 'chartype1', ...]
     }
     list: [ 'chartype1', ...]
   }
   hideCharts: {
      // same structure as addCharts
   }
}

1. bySubcohort{} is chart type list per subcohort, this will be used for profile which has a subcohort-specific chart type we have to support
2. list[] is a flat list
3. both bySubcohort and list can be used at same time

[xzhou82]

may hold this off and coordinate with Airen's efforts