Update Flutter plugin structure; Add support to new Android plugins …

[ewertonrp]

Update the project structure to use the new standards, mainly to update the Android plugin version.

[ewertonrp]

Every year I participate at hacktoberfest This year, the pull requests needs fill one of the requirements bellow:

• Maintainers of the repository can add the "hacktoberfest" topic to their repository
• Add the "hacktoberfest-accepted" label to an individual pull request

Could you please do one of the requirements above? Thanks

Your PR was submitted to a repository that is not participating in Hacktoberfest. Maintainers of the repository can add the "hacktoberfest" topic to their repository if they wish to participate. Alternatively, an individual PR can be opted-in with a maintainer adding the "hacktoberfest-accepted" label to the PR.