[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