DefaultTypeNameFactory: friendly name for generic types (removes assembly qualified name of generic types).

Note: this change breaks existing keys based on source names (generic types only).

	modified:   Localization.Core/DefaultTypeNameFactory.cs
Several improvements:
- Better support of native culture and default culture (native culture can be different of default/fallback culture).
- Adds extension point for missing localized strings (special formatting, etc.).
- Specific behavior for missing localized strings can be skipped.
Update of readme.