bugfix-2.0.x critical fix (#7401)

* Fix mistake in gitignore file and add in missing core files.

The missing leading slash on "lib" meant all folders names lib in the directory tree are ignored, rather than just the top level PlatformIO lib folder

* Add LiquidCrystal Library and associated headers modified to compile.

.gitignore

@@ -122,7 +122,7 @@ tags
 .piolibdeps
 .clang_complete
 .gcc-flags.json
-lib/
+/lib/
 
 #Visual Studio
 *.sln