Update Icons about flutter-icons

[ThinkBIG-Company]

Hello everybody!
Since the libraries here haven't been updated for a long time, I have done this now briefly.
So instead of 3k icons you can now use over 15k icons.
I couldn't update octicons to the last available version because the codepoints are missing.
https://github.com/ThinkBIG-Company/flutter-icons
Love greetings

[Melvin-Abraham]

*Octicons: v10.0.0 (Octicons-v2)

[ThinkBIG-Company]

@juanagu Yes will start working on this now...

[juanagu]

@ThinkBIG-Company any plan to migrate to null safety?

[juanagu]

@juanagu Yes will start working on this now...

Hello, I'm having some problem with the last release, some getters are broken:

                                                 
 Error: Getter not found: 'ios_heart_outline'.
              iconData: Ionicons.ios_heart_outline,

Also all the FlutterIcons._faw now are FlutterIcons._fa I don't know if this change is intentional.

[josephcrowell]

I pushed out a fork which includes all missing icons including Fontisto fonts and jibiel's fixes for null safety support: https://pub.dev/packages/flutter_font_icons