Add support for number symbols of different numbering systems

- Import number symbols for available  numbering systems from cldr data
- Add default_numbering_system  and other_numbering_systems properties for Locale
- Add numbering_system argument to relevant number formatting fuctions and use number symbols based on the given numbering system

Fixes partially issue python-babel#446

babel/core.py

@@ -149,7 +149,7 @@ class Locale:
     `Locale` objects provide access to a collection of locale data, such as
     territory and language names, number and date format patterns, and more:
 
-    >>> locale.number_symbols['decimal']
+    >>> locale.number_symbols['latn']['decimal']
     u'.'
 
     If a locale is requested for which no locale data is available, an
@@ -625,16 +625,39 @@ def currency_symbols(self) -> localedata.LocaleDataDict:
 
     @property
     def number_symbols(self) -> localedata.LocaleDataDict:
-        """Symbols used in number formatting.
+        """Symbols used in number formatting by number system.
 
         .. note:: The format of the value returned may change between
                   Babel versions.
 
-        >>> Locale('fr', 'FR').number_symbols['decimal']
+        >>> Locale('fr', 'FR').number_symbols["latn"]['decimal']
         u','
+        >>> Locale('fa', 'IR').number_symbols["arabext"]['decimal']
+        u'٫'
+        >>> Locale('fa', 'IR').number_symbols["latn"]['decimal']
+        u'.'
         """
         return self._data['number_symbols']
 
+    @property
+    def other_numbering_systems(self) -> localedata.LocaleDataDict:
+        """Mapping of othern numbering systems.
+        >>> Locale('el', 'GR').other_numbering_systems['traditional']
+        u'grek'
+
+        .. note:: The format of the value returned may change between
+                  Babel versions.
+        """
+        return self._data['numbering_systems']
+
+    @property
+    def default_numbering_system(self) -> str:
+        """The default numbering systems used by the locale.
+        >>> Locale('el', 'GR').default_numbering_system
+        u'latn'
+        """
+        return self._data['default_numbering_system']
+
     @property
     def decimal_formats(self) -> localedata.LocaleDataDict:
         """Locale patterns for decimal number formatting.