[pgadmin][patch] Electron version 4.X

Hi Hackers,

Attached you can find the patch that introduces electron to our code base.

What do we provide with this patch:

- Start the pgAdmin server from Electron
- When starting pgAdmin, the user is shown a window that tells them that
pgAdmin is loading.
- Once the server has started, the loading window disappears and opens
pgAdmin in a window
- Desktop user has the ability to open up new windows to work in.
- When you close pgAdmin it properly shuts everything down.
- Stop using copy of web folder for development
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This is the initial patch for people to start paying around with the
electron version. There might be things that are not working.
What we know:
- Logging is not working on windows
- We are not packaging any pg_* executables
- Consistent/Centralized versioning between Electron and pgAdmin Server

We generated builds for:

- MacOs:
https://storage.googleapis.com/pgadmin-binaries/pgAdmin-4.0.4%2Bdev.darwin.zip
- Ubuntu/Debian 64 bit:
https://storage.googleapis.com/pgadmin-binaries/pgAdmin_4.0.4~dev_amd64.linux.zip
- Windows 64 Bit:
https://storage.googleapis.com/pgadmin-binaries/pgAdmin-4.0.5-dev-windows.zip
- Runtime code is still present
- Didn’t update the make scripts

We added some instructions on how to build these 3 binaries in
electron/Readme.md

Thanks
Joao
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