This commit replaces calls to pycompat helpers that were intended for
python 2 <-> python 3 interoperability for python 3 builtins, as python
2 is no longer officially supported by Odoo.

This includes:
    * calls to imap/izip/ifilter replaced by map/zip/filter
    * uses of text_type replaced by str
    * uses of unichr replaced by chr
    * calls to implements_to_string, implements_iterator removed
    * string_types and integer_types replaced by str, int respectively
    * calls to to_native replaced by calls to to_text

This is done in preparation to the removal of these deprecated helpers
in the following commit.

Now that we're closer to switching to P3 for good, these helpers have
outlived their usefulness, and mostly add noise.

All remaining dict.iter*() or dict.view*() must be converted to the
normal keys(), values() or items() calls.

Whenever the result is likely to be used for more than the scope of a
loop, or when the dict needs to be modified during iteration, the calls
must be wrapped in a ``list()``, to protect the new P3 semantics.
Those cases are very exceptional.

Also removed some dead code or improved the API to remove unnecessary
conversions.

* remove references to basestring & unicode (use relevant pycompat
  helpers)
* remove some str calls (either entirely or replaced by relevant
  helper, either text or native)
* use better API to avoid unnecessary conversions
* remove some XML declarations in views

In Python 3:

* various builtins and dict methods were changed to return
  view/iterable objects rather than lists
* and the separate Python 2 view/iterable builtins and methods were
  removed altogether

This is problematic when using these items as list (which the happens
repeatedly in Odoo), but more viciously when iterating *multiple times*
over them (which also happens, which I've messed up multiple times while
writing this, and which is a pain to debug even when you've just created
the issue).

Convert all code using these to semantics-matching cross-version
helper functions to get the LCD behaviour between P2 and P3, and
forbid the builtins via lint.

issue #8530

* in P3, the iterator stepping method has become a dunder method (next
  -> __next__), the protocol has not changed, add a __next__ alias to
  the iterator-next definition (nota: ir.config also has a next method
  but it's not part of an iterator, so don't alias it and don't
  convert calls to it)
* since ~2.6, a builtin (next()) has been added to step an iterator &
  allow for a default (in case of iterator end), convert all manual
  stepping to the builtin

Fixers:
    libfuturize.fixes.fix_next_call

#8530

- remove 2011 tax data
- remove unneeded tax account for 0% taxes
- TVA en amont moved under 421611 instead of 422611
- Fix issues with IB-PA, AP-PA, IP-PA and all taxes with children
- improve structure for tax codes
- fix account type (other -> view)
- add fiscal position mappings
- credit part of IC/EC taxes goes into account 461 instead of 421
- add missing template account for TVA en amont extracommunautaire
- fix a long standing issue with the reconcile flag on accounts
- use TRUE/FALSE instead of t/f in the csv
- added source XLS file with conversion script

Closes #5870