pgAdmin 4 commit: Ship with pre-configured paths that can work inboth

Ship with pre-configured paths that can work in both Server and Desktop modes out of the box. Fixes #2662

Ship the web code using server mode with appropriate paths by default and enable the runtime to override the mode, and
forceinto desktop changing the appropriate paths to user-specific ones. 

Note that this change will likely cause more advanced users to have to tweak configs.

RPMs will also need changes to create /var/lib/pgadmin and /var/log/pgadmin, owned by the webserver account.

Branch
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master

Details
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https://git.postgresql.org/gitweb?p=pgadmin4.git;a=commitdiff;h=f195b18f2d9145592ae60c55840405dc3dfc8ea6

Modified Files
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runtime/Server.cpp         |   3 +-
web/config.py              | 106 +++++++++++++++++++++++++++------------------
web/pgAdmin4.py            |  11 +++++
web/regression/runtests.py |  11 +++++
4 files changed, 89 insertions(+), 42 deletions(-)