[pgAdmin][RM4701] Webpack optimization

Hi Hackers,

Attached is the patch to optimise webpack bundled files for improving
performance.
@Ashesh Vashi <ashesh(dot)vashi(at)enterprisedb(dot)com> Thank you for your
suggestions and inputs.

Changes include:
1) Remove underscore-string and sprintf-js packages as we were using only
%s. Instead, added a function to do the same. Also changed gettext to
behave like sprintf directly.
2) backgrid.sizeable.columns was not used anywhere, removed.
@babel/polyfill is deprecated, replaced it with core-js.
3) Moved few css to make sure they get minified and bundled.
4) Added Flask-Compress to send static files as compressed gzip. This will
reduce network traffic and improve initial load time for pgAdmin.
5) Split few JS files to make code reusable.
6) Lazy load few modules like leaflet, wkx is required only if geometry
viewer is opened. snapsvg loaded only when explain plan is executed. This
will improve sqleditor initial opening time.

Below is the size and files difference after and before the changes:
[image: Screenshot 2019-09-18 at 14.13.02.png][image: Screenshot 2019-09-18
at 14.04.41.png]
Below is the lighthouse (Chrome extension) report after and before the
changes:
[image: Screenshot 2019-09-18 at 13.53.10.png] [image: Screenshot
2019-09-18 at 14.08.20.png]

Do not forget to do a yarn install and a pip install
Kindly review.

--
Thanks and Regards,
Aditya Toshniwal
Software Engineer | EnterpriseDB India | Pune
"Don't Complain about Heat, Plant a TREE"