Add element wise logistic regression cost function

  E = - \sum_{i,j} y[i,j] log( \hat{y}[i,j] ) + (1 - y[i,j]) log( 1 - \hat{y}[i,j] )

  Make it numerical stable,
  \hat{y}[i,j] = logistic( z[i,j])
  where z[i,j] is the previous layers activation
  + computeEltwiseLogregCost
  + computeEltwiseLogregGrad
  + EltwiseLogregCostLayer