Let $f:\mathbb{R}\to\mathbb{R}$ be a function defined by $f(x)=(2+3a)x^{2}+\dfrac{a+2}{a-1}x+b$, $a\ne1$. If $f(x+y)=f(x)+f(y)+1-\dfrac{2}{7}xy$, then the value of $28\displaystyle\sum_{i=1}^{5}\lvert f(i)\rvert$ is