[dev] [en] i18n and dynamic menu changes

[Goffi]

G'day,

there are again some important changes in core, concerning 
internationalisation (i18n) and dynamic menus:


*** i18n ***

	- _() method is not imported anymore in __builtins__ but has to be 
explicitly imported from sat.core.i18n. I think it's more clean, and it 
avoid errors with tools like pyflakes.
	
	- core.i18n module manage gettext importError, thus is can be used in 
Libervia directly

	- there id a D_() method for deferred translation. This need some 
explanations: xgettext read python sources to find _() method to get 
sentences to translate. But xgettext only get python strings. In 
addition the _() method return the translated string immediately, this 
is not always what we want. D_() allow to say "I want to translate this 
sentence, but I'll do it later, so keep the sentence untranslated for now".
	Two usecases to be more clear:

		* if you have a constants that has to be used for a parameter 
category, you want to keep the sentence untranslated, until you actually 
display it. This is what is used in 
plugins/plugin_misc_text_syntaxes.py: the CATEGORY constant is a 
deferred translation like this: CATEGORY = D_("Composition") .
	After, the untranslated version is used in TextSyntaxes.params for 
category_name (CATEGORY), and the translated one is used for 
category_label (_(CATEGORY))

		* if you want to dynamically translate a sentence in a other language. 
This is the case for menus: Libervia can be used by people speaking 
different languages at the same time, so menus need to be translated on 
the fly. the getMenus bridge method take a language argument to select 
the language.

		When using importMenu, you need to give deferred translation for that 
(e.g.: (D_('Open'), D_('File')). The untranslated version is used to 
check conflicts, while the translated version is returned to the 
frontend with menu_path_i18n.

	- to do dynamic translations, you can change the translation language 
with core.i18n.languageSwitch (dont forget to change back to default 
after ! Just use languageSwitch() with no argument)


** menus **

	- menus now use generic callback system. When using importMenu, you can 
give an actual callback, or the id of an already registered callback (in 
this case, you can use additionnal *args and **kwargs as allowed by 
registerCallback).

	- the extra data parameter is used by menu. e.g. the selected jid for 
ITEM_CONTEXT is returned throught these data, with the "jid" key.

	- menus are now identified with menu_id (same as callback_id) instead 
of (type, category, name) tuples

	- paths (array of strings) are used instead of category/name.
	  e.g. instead of the category "File" and the name "Open", we use the 
path ("File", "Open"). This allow to easily create submenus.

	- menus are internationalised (see above)

	- security_limit is used in the same ways as for parameters.

Next week I will not be available a lot, so the 0.4 is postponed to 
begin of january. I still need to refactor XMLUI and fix gateways 
(XEP-0100).

Cheer
Goffi