Do not call app() to get access to acl_users.

app() creates a new transactional connection to ZODB, which triggers
scary (although innocuous in this case) connection pool warnings.
Instead, use getSite provided in ERP5 product and filled when
traversing site's portal. Retrieved acl_users object is different, but
this should not matter.
Also, to prevent import loop and to keep this change minimal, do a
local import.
Fix runUnitTest for Zope 2.13 by disabling ZopeLite patches

A ZopeLite patch was added to prevent loading of zcml files, which is wrong
for ERP5: CMF products were not properly initialized.

Code is also simpler now that we call OFS.Application.initialize(), which is
not significantly slower.

We keep patch not to register help though because this is quite expensive:
we should even consider always disable help because they seems to cause many
conflicts during Zope cluster startup.

A monkey-patch to unittest is updated for Python 2.7, so that tests aren't run
when they shouldn't (e.g. --save without --load).
DemoStorage: update conflict resolution patch for ZODB 3.10
Fix random failure of testConflictResolution.TestERP5.testActiveProcess
Fix test_getPropertyForUid now that runUnitTest installs portal_uidhandler

See commit 4718f5e11be8f2541dc8f6876cd60aa03d0edc76
Remove obsolete code from testDeferredStyle
testPDFForm: zope.app.testing is deprecated
Define property's default value at class level.
Simplify code.

Doc's mention about expiration time is precisely that server's code is
supposed to do just that internally.
Drop unused global and duplicate import.
Simplify pseudo-constants' value.
Drop meaningless default values.

Simplifies code creating a new connection.
Drop TODOs.

Concurrency handling is not required, because a single MemcachedDict should
not be accessed outside a Zope transaction, which is itself bound to a
specific thread.
Pickling a connection is not needed, ERP5Type.Core.MemcachedPlugin is all
we need to serialise.
Factorise class declaration.
Drop dummy method not present on actual implementation.
Initialise MemcacheTool class.
Drop traceback import.
Inline code documentation.

Docstrings are not to annotate what code is doing.
Factorise end-of-transaction cleanup code.
Make SharedDict a new-style class.