* added `composer.json` to allow fetching of SlickGrid as `composer` package

* feat(plugins): add header/grid menu item "hidden" property
- in some cases we might want to use "disabled" but in other cases we might want to use "hidden"

* refactor(plugins): add "hidden" property to HeaderButton plugin as well

* refactor(plugins): add "hidden" property to all plugins with menu items

* refacor(plugins): add "hidden" property everywhere potentially called

* Feature:TotalCount in Pager - it's now possible to show the number of rows (and begin and end position) in pager

Co-authored-by: arash dalir <[email protected]>
Co-authored-by: ghiscoding <[email protected]>

Now, if the dropped column header contains an element with class 'slick-column-name', only the text content of that element is used to populate the dropped grouping represenation. This prevents additional column header content from being displayed (like the order number in case of sorting by multiple columns).

- this will help in calculation our own column widths and calling `reRenderColumns` to resize columns accordingly

- fixes #582
- the original issue only mentioned the HeaderMenu plugin but I went ahead and applied the same logic (and tested them all) on the following plugins
   - HeaderMenu
   - GridMenu
   - ContextMenu
   - CellMenu

…r visibility (#591)

* Two changes made for better support for frozen columns with column reordering enabled.

slick.draggablegrouping.js 
Only one header's ids were being accounted for after a drag and drop reorder when columns were frozen. the result is that the left (frozen) columns were fine, but the right (unfrozen) columns were 1) not sorted, and b) turned off.

slick.grid.js
Similar to the draggablegrouping issue, the grid was not honoring the preheader state for the unfrozen columns because only hte preheaderPanelScroller was  being updated setPreHeaderPanelVisibility. For me this showed itself because I had teh preheader row toggled off and froze some columns and the headers disappeared for my unfrozen columns due to the preheader row being visible but empty and the headers being under the first row of data.

* Updated draggableGrouping changes with comments and added fixes that properly use ids.header.sortable("toArray") as the array to loop on.

* changed ctr to headerI for better clarity.

* further correction to second for loop, it should have been pushing from the ids variable rather than header variable.

I also renamed headerI2 to idI and l2 to idL for the index and length variables in the for loop.

* corrected for hiding rather than slideDown for non visible non animated right column.

…d if there are multiple grids. (#593)

* To Fix the issue specific to drag selection in non-frozen part of grid if there are multiple grids.

Issue Description: if we have multiple grids in same page/in the DOM, the above code looks for  '.grid-canvas-left' width which indeed gets the result of the grid where the event triggered and the other grids present in the DOM. If the action is done on second grid(which has frozen column) instead of first one above code is getting the width of first grid instead of second one. So made changes to get the width only for the event triggered grid.

* As per request changed the syntax to ES5 to support legacy browser

- the available `target` options will be: "grid" or "composite"
 - since we can also use the `onBeforeEditCell` event within the Composite Editor, I needed a way to make a distinction between a call made with `onBeforeEditCell` from the grid or from the composite component. This `target` will let me know where it was executed from.

- since SlickGrid can be used in other libs and components, it could be useful to be more explicite from where the error originated, add SlickGrid prefixes to all error messages