Replaced image formulas with the MathJax ones

docs.it4i/snippets/fairshare_formula.md

+$$
+MAX\_FAIRSHARE * ( 1 - \frac{usage_{Project}}{usage_{Total}} )
+$$

docs.it4i/snippets/job_sort_formula.md

+$$
+1000*queue\_priority + \frac{fairshare\_priority}{1000} + \frac{eligible\_time}{864000}
+$$