pgAdmin 4 commit: Basic setup for auto update implemented.

Basic setup for auto update implemented.
TODO:
1) Change the update check URL per pgadmin.org
2) Put everyting in README on how to test in dev

Branch
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electron2

Details
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https://git.postgresql.org/gitweb?p=pgadmin4.git;a=commitdiff;h=063c29fd7664a2ed0535da6a515ad41f5810fab1

Modified Files
--------------
Makefile                            |   3 +
electron/.eslintrc.js               |   1 +
electron/package.json               |  15 +++--
electron/src/check_python_server.js |  13 ++--
electron/src/dev-app-update.yml     |   4 ++
electron/src/index.js               |  35 +++++++---
electron/src/logger.js              |  17 +++--
electron/src/updater.js             |  77 ++++++++++++++++++++++
electron/yarn.lock                  | 123 +++++++++++++++++++-----------------
pkg/mac/build-electron.sh           |  68 ++++++++++++++++++++
pkg/yarn.lock                       |   4 ++
yarn.lock                           |   4 ++
12 files changed, 284 insertions(+), 80 deletions(-)