Improve usability on macOS including altering shortcuts

This change removes some application attributes that are not necessary anymore (like disabling the global menu bar) or make Konsole behave slightly different when used from a KPart (e.g. inside Kate), and changes some keyboard shortcuts around (mainly using Command instead of Ctrl+Shift now.)

Unfortunately this does not resolve the requirement for the special keytab file for macOS; it looks like Qt does something funny with the QKeyEvents here: on Linux these have a `text` attribute set to e.g. `\u0003` for `^C`, that attribute is empty on macOS.

Note this could impact shortcut changes on non-macOS systems.