Flags not in package handling

[bounty1342]

• Reduce svg version No need to increase for minor version with ^, avoid compatibility issue with other libs
• Add static list of flagsCode fix #30
• Add replacement widget, in case flag not in list avoid generating an error, if they want same layout, they can do Container(width: width, height: height,)
• Add default replacement widget default is to not take space or memory
• Update example

[LunaGao]

Thank you. @bounty1342