Add default values for verticalMarginUnit and cellHeightUnit, update readme to have verticalMargin info, and several more unit tests.

Author: radiolips

dist/gridstack.js

@@ -537,7 +537,9 @@
             disableResize: opts.disableResize || false,
             rtl: 'auto',
             removable: false,
-            removeTimeout: 2000
+            removeTimeout: 2000,
+            verticalMarginUnit: 'px',
+            cellHeightUnit: 'px'
         });
 
         if (this.opts.rtl === 'auto') {

dist/gridstack.min.js

@@ -48,6 +48,7 @@ gridstack.js API
   - [setGridWidth(gridWidth, doNotPropagate)](#setgridwidthgridwidth-donotpropagate)
   - [setStatic(staticValue)](#setstaticstaticvalue)
   - [update(el, x, y, width, height)](#updateel-x-y-width-height)
+  - [verticalMargin(value, noUpdate)](#verticalmarginvalue-noupdate)
   - [willItFit(x, y, width, height, autoPosition)](#willitfitx-y-width-height-autoposition)
 - [Utils](#utils)
   - [GridStackUI.Utils.sort(nodes[, dir[, width]])](#gridstackuiutilssortnodes-dir-width)
@@ -438,6 +439,13 @@ Parameters:
 
 Updates widget position/size.
 
+### verticalMargin(value, noUpdate)
+
+Parameters:
+
+- `value` - new vertical margin value.
+- `noUpdate` - if true, styles will not be updated.
+
 ### willItFit(x, y, width, height, autoPosition)
 
 Returns `true` if the `height` of the grid will be less the vertical constraint. Always returns `true` if grid doesn't