-use of the override keyword
-delete unused code
-const correctness
-more uniform code style
-for each with const references when possible
-getters no longer use the word 'get'
-others
The controller class has some important methods which may be
required in multiple parts of the code. Now that class is a
singleton (that may change in the future).
The core parts have been moved to src/core.
Now the tray Icon can be disabled by the controller.
I need to reimplement a new notification system due to its
dependency with the tray icon, they are disabled in this actual
commit.
