Fix padding of workspace thumbnails in overview

[mzur]

The workspace thumbnails in the overview should have vertical padding (same as horizontal). Maybe related to #177

[ebeem]

You're right, I think it's related to #177
The reason behind that is because we actually have lists in the WorkspaceSwitcherPopupList equal to the amount of rows we have in wsmatrix. Long story with the limitation faced while implementing a grid in the WorkspaceSwitcherPopupList.

I think to fix this, we need to build a St.ScrollView to contain a single list which has all the workspaces.
In other words, _lists should be one list instead of a array of lists

gnome-shell-wsmatrix/wsmatrix@martin.zurowietz.de/workspacePopup/workspaceSwitcherPopupList.js

Lines 29 to 47 in 64c3895

	var WorkspaceSwitcherPopupList = GObject.registerClass({
	Signals: {
	'item-activated': {param_types: [GObject.TYPE_INT]},
	'item-entered': {param_types: [GObject.TYPE_INT]},
	'item-removed': {param_types: [GObject.TYPE_INT]}
	},
	}, class WorkspaceSwitcherPopupList extends St.BoxLayout {
	_init(thumbnails, workspaceName, options) {
	super._init({
	style_class: 'switcher-list',
	vertical: true,
	style: `spacing: ${ITEM_SPACING}`,
	});
	this._lists = [];
	this._thumbnails = thumbnails;
	this._workspaceName = workspaceName;
	this._scale = options.scale;
	this._showThumbnails = options.showThumbnails;
	this._showWorkspaceName = options.showWorkspaceNames;

I think this issue is a high priority as it will help a lot in styling and most likely contribute to fixing #182