Resolve "ggplot2 and WRTDSplus Visualization Vignette"

Closes #16 (closed)

Updates,

• Added function ConcQSmoothplus() that can take WRTDSplus models with an additional variable and/or a replaced discharge variable and return a dataframe that can be used to create a plot similar to plots produced by EGRET::plotConcQSmooth().
• Added function ConcTimeSmoothplus() that can take WRTDSplus models with an additional variable and/or a replaced discharge variable and return a dataframe that can be used to create a plot similar to plots produced by EGRET::plotConcTimeSmooth().
• Added a vignette that gives examples of plots that maybe helpful to visualize data and results from WRTDSplus models. This vignette uses the results from the workflow 1 vignette for all example plots. The results from that vignette were saved here vignettes/MS-BELL_eList_Est.rds