Add a font size / whole editor zoom button to statusbar

[tomlin7]

Feature

Like in visual studio, this might be a helpful addition, maybe? This can also be a slider (or will that look weird?)
If going for a list of values like 25%, 50%, 75%, 100%, custom value the command palette can be used to pick the values.

comment any further suggestions and ideas you guys have!

notes

• statusbar class, this also demonstrates the implementation of command palette actionsets.
• the base class can be accessed from any class like self.base, the base class holds reference to all other components of the editor including the layout.
  eg. settings can be accessed like self.base.settings. active editor can be accessed like self.base.editorsmanager.active_editor
• globally used fonts can be accessed from settings class