Add warning in the plotMap function

[IsabelleBailleul]

Some warnings should be added in the plotMap function.

At least the two following points have been identified :

• if the mcYear filled in the argument "mcYear" is not loaded in the antaresData to plot, no warning is issued whereas another mcYear is used
• if a variable is filled in for the argument "sizeAreaVars" and does not exist in the antaresData to plot, the function does not issue any warning and plots something anyway, while the legend gets mixed up because of this non existant variable