simplify error handling and avoid code duplication (thanks Romain for advices)

Instead of trying without and retry in case of TypeError, we now have a reliable
rule: aq_parent is passed if and only if the name of first argument is 'self'.

The main optimization is the replacement of
  erp5.component.extension.find_load_module
by a simple
  __import__
like it was before commit c2ce3ba0

Use it on PythonScript & ExternalMethod.

- Code refactoring and small optimizations.
- Really fix unwanted acquisition.
- ExternalMethod: fix security declarations.
- Fix role/permission checking for ExternalMethod called by a PythonScript
  with proxy roles.
- When editing an existing guard, modify it instead of always recreate one.
  no very useful here, but that's good practice: this is nicer for the ZODB
  and it's easier to browse the history. BT should do the same when upgrading.

If for some reasons, this gadget does not get results (usually due to network failures or
service unavailable for other reasons), do not fail and retry until it works again

To be consistent with other type information classes such as
SolverTypeInformation or PDFTypeInformation.

At the same time, describe a bit more

- use `obj.data` instead of `str(obj)` to get File object content
- fix data_uri split unpack issue
- fix str/unicode encoding errors
- fix allow parse url list in css

erp5_upgrader: TemplateTool_checkCategoryNameConsistency constraint can update categories which have moved

[erp5_web_renderjs_ui] Update website modification, to prevent launcher gadget modification date to be more recent

- WebPage_exportAsSingleFile
- WebPage_extractReferredObjectDict

when converting an image, the returned value of img.convert
is not everytime a string. It might be a kind of acquisition
value

testTask: new test to check that simulation inheritance can overwrite default ledgers set on portal type

testAccounting: makes test_createBalanceOnLedgerWithTransactionsWithNoLedger closer from Delivery Type expected behaviour

Add allow_tag_list and deny_tag_list parameter to WebPage_extractReferredObjectDict

HTML rendering tolerates list value, and renders are multi-lines.
Do the same in ODT renderer.

disable derived_merge in a query where it may cause the wrong result, instead of using DISTINCT trick.

* normalize URL in a case where we have several languages in URL.
* redirect to the web site root if HTTP_REFERER is not set.