Apply Flutter best practices [Non-Breaking] (#2)

* Add flutter_lints package

* Use key in widget constructors

lint: use_key_in_widget_constructors

* Unnecessary new keyword

lint: unnecessary_new

* Prefer const with constant constructors

* Exclude protobuf files from analyzer

* Private field could be final

* Annotate overridden members

* Use initializing formals when possible

* Don't access members with `this` unless avoiding shadowing

* Prefer is! operator

* Use isEmpty instead of length

* Use collection literals when possible

* Revert comment changes

* Cleaner null testing

* Misc fixes

* Avoid using `forEach` with a function literal

* Prefer `final` over `var` where applicable

* Enforce stricter type-checking

* Ignore VS Code files

* Flutter format

* Prefer using lowerCamelCase for constant names

* flutter format -l 100

* Disable `avoid_print` for examples

* Slight improvements to example

Should solve lint error: no_logic_in_create_state

lib/src/track/track_publication.dart

@@ -21,15 +21,14 @@ class TrackPublication {
     updateFromInfo(info);
   }
 
-  /// True when the track is published with name [Track.ScreenShareName].
-  bool get isScreenShare =>
-      kind == TrackType.VIDEO && name == Track.ScreenShareName;
+  /// True when the track is published with name [Track.screenShareName].
+  bool get isScreenShare => kind == TrackType.VIDEO && name == Track.screenShareName;
 
-  updateFromInfo(TrackInfo info) {
+  void updateFromInfo(TrackInfo info) {
     muted = info.muted;
     simulcasted = info.simulcast;
     if (info.type == TrackType.VIDEO) {
-      dimension = new TrackDimension(info.width, info.height);
+      dimension = TrackDimension(info.width, info.height);
     }
   }
 }