Updates all example projects to build as universal binaries that run on
both armv7 and arm64 now that we support both platforms on iOS.

This consolidates all of the non-template .gitignore rules into the top level .gitignore, to ignore common things more broadly, with less maintenance needed for the .gitignore files. Does not touch the templates, so that they still produce needed .gitignores as part of flutter create.

Under android/ directory, ignore:
GeneratedPluginRegistrant.java

Under ios/ directory, ignore:
GeneratedPluginRegistrant.h
GeneratedPluginRegistrant.m
Pods/

* Add Pods cache dir to ios/.gitngnore

* Add missing ending newlines

* wip

* wip

* delete main.m

* readd main.m

* update to use new channel api

* update android

* removed android/

* remove debug print

* remomved main.m

* Update year in copyright

* break long line and update name

* mit comments

* update examples/README

* break line

* update README

* update test