pgAdmin 4 commit: Initial version of the new tree implementation.

Initial version of the new tree implementation.

This is the first version of our Tree implementation. At this point is a
very simple tree without no abstractions and with code that eventually
is not very performant, but this is only the first iteration and we are
trying to follow the 'Last Responsible Moment Principle' [1].

Implemention details:
- Creation of PGBrowser.treeMenu
- Initial version of the Tree Adaptor 'pgadmin/static/js/tree/tree.js'
- TreeFake test double that can replace the Tree for testing purposes
- Tests, As an interesting asside because Fake’s need to behave like
the real object you will noticed that there are tests for this type
of double and they the same as of the real object.

[1] https://medium.com/@aidanjcasey/guiding-principles-for-an-evolutionary-software-architecture-b6dc2cb24680

Patched by: Victoria && Joao
Reviewed by: Khushboo & Ashesh

Branch
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master

Details
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https://git.postgresql.org/gitweb?p=pgadmin4.git;a=commitdiff;h=bc4d16eb8333ff0e611146e1cb83443b7da55eba
Author: Joao De Almeida Pereira <jdealmeidapereira(at)pivotal(dot)io>

Modified Files
--------------
web/pgadmin/browser/static/js/browser.js | 4 +
web/pgadmin/static/js/tree/tree.js | 212 ++++++++++++++
web/regression/javascript/tree/tree_fake.js | 69 +++++
web/regression/javascript/tree/tree_spec.js | 420 ++++++++++++++++++++++++++++
4 files changed, 705 insertions(+)