Changes the main interface, adds persistent settings

- Menu bar items
-- Source Estab: Open, Open Recent, Save As
-- Target Estab: Create, Open, Open Recent, Save, Save As
-- View: choose components visibility, change the estab editors position

- Moves copy and save buttons to a toolbar

- Settings can be loaded and saved to estab-settings.xml
-- Saved settings: window geometry, recent opened files, components visibility
Creates default settings file, saves panel position
Merge branch 'feature/main-gui' into develop