pgAdmin 4 commit: Do not use the sqlite for session handling, as the ol

Do not use the sqlite for session handling, as the old implementation is
optimized to work from multiple threads. It has too many frequent
transaction from multiple threads, and that tends to result into the
'database is locked' error of sqlite.

With the new implemenation, we're using the caching mechanism, which
keep the data in the memory all the time, and saves it on request
completion, and loads it only for the first time. Also, it will storage
the data using pickle, which will be faster than accessing sqlite.

Fixes #1329

Branch
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master

Details
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http://git.postgresql.org/gitweb?p=pgadmin4.git;a=commitdiff;h=61698b7b4db3eea39a034c7ff0f90d0c710ffcb8

Modified Files
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requirements_py2.txt         |   1 +
web/pgadmin/__init__.py      |   4 +-
web/pgadmin/utils/session.py | 424 +++++++++++++++++++++++--------------------
3 files changed, 234 insertions(+), 195 deletions(-)