undid tags as set, to rather in a twig

Author: Affie

src/entities/DFGFactor.jl

@@ -47,7 +47,7 @@ mutable struct DFGFactor{T, S} <: AbstractDFGFactor
     timestamp::DateTime
     """Factor tags, e.g [:FACTOR].
     Accessors: `getTags`, `addTags!`, and `deleteTags!`"""
-    tags::Set{Symbol}#Vector{Symbol} #TODO I propose we use a set since tags can't be repeated.
+    tags::Vector{Symbol}
     """Solver data.
     Accessors: `getSolverData`, `setSolverData!`"""
     solverData::GenericFunctionNodeData{T, S}

src/entities/DFGVariable.jl

@@ -20,7 +20,7 @@ struct DFGVariable{T<:InferenceVariable} <: AbstractDFGVariable
     timestamp::DateTime
     """Variable tags, e.g [:POSE, :VARIABLE, and :LANDMARK].
     Accessors: `getTags`, `addTags!`, and `deleteTags!`"""
-    tags::tags::Set{Symbol}#Vector{Symbol} #TODO I propose we use a set since tags can't be repeated.
+    tags::Vector{Symbol}
     """Dictionary of estimates keyed by solverDataDict keys
     Accessors: `addEstimate!`, `updateEstimate!`, and `deleteEstimate!`"""
     ppeDict::Dict{Symbol, <: AbstractPointParametricEst}