The figure below depicts a regular $7$-gon inscribed in a unit circle. What is the sum of the $4$th powers of the lengths of all $21$ of its edges and diagonals? $\textbf{(A) }49 \qquad$ $ \textbf{(B) }98 \qquad$ $ \textbf{(C) }147 \qquad$ $ \textbf{(D) }168 \qquad$ $ \textbf{(E) }196$