Add flexible grid column width handling into LayoutManager

And here's the follow-up. Unfortunately, the regions also rely on that grid css.
As I don't know a better way to access the current number of columns of the grid in Region.prototype.alterSpan() I added those now as parameter :|
If there's an easier way to access that information the patch would be smaller ;)
However, the approach is the same -> calculate the width as percentage.

Ooops, there was still an issue in the previous patch.
Fixed missing isRelative parameter in one of the modified calls.

Further I noticed that LayoutStep.prototype.startRegionResize() seems to calculate odd data.
Thus I've that patched as well:

• Use this.$editor.width() to calculate the frame width - this is the effective value and not the "it should be like defined in the step" one ;) (Had some trouble with margins)
• Added values that define where the most left / right columns of the region are
• Changed max left / right traversal values. I think they make more sense now - e.g. if you drag the right handle to the left you shouldn't be allowed to make the region smaller than 1 column.

     LayoutStep.prototype.modifyRegionBuild = function ($region) {
@@ -122,16 +122,18 @@
       });
       // Calculate the column size so regions can be snapped to grid columns.
       data.totalColumns = Number(this.grid.info('columns'));
-      data.frame = Math.floor(Number(this.step.info('size')) / data.totalColumns);
+      data.frame = Math.floor(Number(this.$editor.width()) / data.totalColumns);
       // Store the X origin of the original click.
       data.originX = event.pageX;
       // Get the column the resize started in.
       widthOffset = (data.side === 'right') ? data.width : 0;
       originalColumn = Math.floor(($region.position().left + widthOffset) / data.frame);
       data.originColumn = (data.side === 'left') ? ++originalColumn : originalColumn;
+      data.leftColumn = Math.ceil($region.position().left / data.frame) + 1;
+      data.rightColumn = Math.ceil(data.leftColumn + (data.width / data.frame));
       // Calculate the left and right bounds for the resizing.
-      data.rightMaxTraversal = data.totalColumns - data.originColumn;
-      data.leftMaxTraversal = (data.originColumn -1) * -1;
+      data.rightMaxTraversal = (data.side === 'left') ? ((data.rightColumn - data.leftColumn - 1)) : ((data.totalColumns - data.rightColumn + 1));
+      data.leftMaxTraversal = (data.side === 'right') ? ((data.rightColumn - data.leftColumn - 1) * -1) : (data.leftColumn - 1) * -1;
       // Add behaviors.

Oh, lost my patch :|