[pgAdmin4][Patch]: Adding connection status in Query tool

Hi,

PFA patch to add the connection status in query tool, this feature will allow user to check the database connection status in query tool itself, it will also provide the detailed status as a tooltip when user hovers on it, the most benefit of the feature will be when user open query tool in new Browser Tab where Browser tree is not visible to user, user can also configure the status polling time using preference dialog.

RM#2475

Apart from that I have also removed the ..sqleditor/static/css/sqleditor.css reference from ../datagrid/templates/datagrid/index.html file because we are already bundling the "sqleditor.css" file in main "style.css" file.