feat(ui5-table): add "loadMore" capability

[ilhan007]

Change
Adds "loadMore" capability to the Table through a special row, displayed at the bottom as first part of the following requirement #2570 At later point, the loadMore capability will be available upon scroll as well.

Usage

• set "has-more" to get the special row at the table's bottom
• listen to the "load-more"event to load more rows, when the user presses the additional row

<ui5-table id="myTable" has-more></ui5-table>

myTable.addEventListener("load-more", function() {
    rowsToLoad.forEach(() => {
	tbl.appendChild(document.createElement('ui5-table-row'));
    );
});

Properties

• hasMore - defines if the load more row will be displayed
• loadMoreText - defines the main text of the load more row ("More" by default)
• loadMoreSubtext - defines a subtext of the load more row (usually info about the number of rows - 4 of 10, 4/10, etc.)

Events

• loadMore - fired when the load more row is pressed

Result

[vladitasev]

I think this description is too technical (the implementation is with a row) but anyway we'll change this text once we add the growing feature as it would need to say "shows a more button or activates the even on scroll" then. I would suggest for now:

Defines if a "More" button will be displayed at the bottom of the table.
Pressing this button will fire the load-more event.