Improve convex hull check

[mhungen]

The current implementation of the convex hull check is inefficient due to the incorrect use of HashMap.
Instead of checking if there is a key O(1) in the set, it checks if the map contains a value O(n).
I think this is an implementation error as previous commits mention a HashSet, which makes sense to me.

/*
 * Second check : be sure input is within the approximated convex hull (see ATBD)
 */

if (bandMinMax != null && definitionGridMap != null) {
    int [] gridProjection = new int[definitionGridSize];
    String gridProjString="";
    for (int i = 0; i < gridProjection.length; i++) {
        double bandMin = bandMinMax[0][i];
        double bandMax = bandMinMax[1][i];
        gridProjection[i] = (int)Math.floor(10 * (input[i] - bandMin) / (bandMax - bandMin) + 1);
        gridProjString+=String.valueOf(gridProjection[i]);
    }
    boolean insideDefinitionDomain = false;
    if(definitionGridMap.containsValue(gridProjString)){  // << here is the problem
        insideDefinitionDomain = true;
    }
    if (!insideDefinitionDomain) {
        setInputOutOfRange(result);
        return;
    }

}

I'm also not a fan of converting each domain definition point to a string representation, which will be hashed again to get an int representation. i suggest combining the int array into a single int and using that as a hash instead.

I also added a comment describing how the check works, because it took me a while to figure out that DefinitionDomain_Grid contains all valid points and not the points of the hull boundary (even though ‘Domain’ should have given me the hint).