* There was another level of cache in Account_hashGapItemList
* Category title was used in AccountModule_getAvailableGapList

Unlike other database adaptors, memcache adaptors can be shared among
transactions. So pool them in order to reduce the number of connections
established to memcached servers. And as the connections handle
thread-safety internally (by inheriting from threading.local), threads
can share the same connection instance.
Also, do not create a new connector each time we get disconnected, just
reconnect.
Also, memcached internally retries connection, so no need to retry it
ourselves.
Also, do not log when failing to update & delete entries in cache
server: this is a racy cache, each read much be checked anyway, so
failed writes are just business as usual.
Also, document a bit more why we catch "any" exception happening during
finish, and specify base exception class following python coding best
practices.
Also, use named constant for loggin levels for remaining log directives.
Also, display traceback when catching a connection issue during
__getitem__, as the original exception gets converted into a KeyError.

/reviewed-on nexedi/erp5!305

By default in ERP5 all fields are not mandatory

Add transparent SVG and PNG icons to the manifest,
rename all functions following the Nexedi conventions,
link to the TodoMVC homepage, move Handlebars template to head,
and rename all files from tutorial_officejs_* to officejs_todomvc_*.

Fixes failing tests because of always showing "No work to be done" in worklist (lazy bug)

Test Results 20170621-6D7F8E4B

/reviewed-on nexedi/erp5!304

/reviewed-on nexedi/erp5!303

/reviewed-on nexedi/erp5!302

Name is unchanged, but it will use
Products.ERP5Type.Utils.checkPythonSourceCode which uses pylint.

The condition for an organisation to be able to use bank account from
other organisations higher in the group hierarchy should not be the
presence of bank account in this organisation, but whether or not it
acts as an independant accounting entity, and this is defined by the
presence of accounting periods.

@Tyagov @luke 

/reviewed-on nexedi/erp5!288

getObject is not public API. Bonus is we can do one query for all uids

Since it's allowed for multiple sections from same group to post
transactions on the bank account from the parent sections, the bank
reconciliation should use the same logic to be able to reconcile
transactions from any section.

( and AccountingTransaction_getDestinationPaymentItemList )

772033ed removed
`parent_strict_group_uid` related key and added support to generate
`strict_parent_group_uid` related key

If rows have been deleted before, it's more natural to simply INSERT and
no need for REPLACE

since predicate is scriptable, a document that was once a predicate may
no longer be a predicate next time it's indexed, so we should remove it
from predicate table in that case.

predicate_category was already doing this correctly

/reviewed-on nexedi/erp5!291

@Tyagov @luke 

During development of JupyterCompile several functions have been used and then removed but their portal_skins remain in ERP5. The purpose of this MR is to remove those skins, since they do nothing. The skins in question are Base_displayHTML, Base_displayImage, Base_saveImage, Base_updateLocalVariableDict and getError.

/reviewed-on nexedi/erp5!289

@Tyagov @kirr 

When someone imported a module in Jupyter they would get a warning for every module they imported like:

    WARNING: Your imported from the module numpy without...
    WARNING: Your imported from the module datetime without...
    ...

This fix shortens those to just one warning at the end of output like so:

    WARNING: You imported from the modules numpy, datetime, ... without ...



/reviewed-on nexedi/erp5!278