Update cosy fox file for SHMS

Added file shms-2017-26cm-monte_quads_p18.fox
Change effective lengths of quads to match
measured values;
    LBE := 0.80 ;              {Effective length of bender}
    L1E := 1.873 ;              {Effective length of Q1}
    L2E := 1.587 ;               {Effective length of Q2}
    L3E := 1.587 ;               {Effective length of Q3}

modified from 9.187419156 to 9.06924

and increased quad fields by 1.8% to
reflect data that found that the dipole
was off by 1.8% when setting it.

   Q1 := -2.136856 ;
   Q2 :=  4.527000 ;
   Q3 := -2.954160 ;