chore(linter): migrated to flutter_lints with additional rules

[daadu]

No description provided.

[daadu]

@WieFel Could replace the current "analyze" action with one that fails it the linter rules are not followed. Current one count the "pub score". What do you think?

This package needs a breather - haven't touched it for a while. Will start with fixing all lint issues - check #100.

[daadu]

The CI steps that are in my mind as of now:

1. analyze - fails if linter rules are not followed
2. widget test - run flutter widget test
3. build example and demo app - check if no issue in building it
4. integration test - run integration test against example and demo app

What do you think about it? You got time this days?

[WieFel]

@daadu you're completely right!
I am currently totally busy :(
But I will be able to review PRs, if needed, or maybe do some very small tasks if we manage to split up the work ;)