New function "Delete line(s)" and other changes

* Added function "Delete line(s)"
* Added menu entry and keyboard shortcut option for:
* "Save All"
* "Find Next"
* "Find Previous"
* Function "Go to line" reacts on Return key
* Removed feature "compile unsaved save".
Compiling unsaved files appear unsaved in the front end.
* Changed handling of config read error:
Silently discard error and continue reading.
* Set focus on start to text input
* Added opt-in feature "Save all on compile"
* Changed main window title to
"file - Aporia" (saved) or "file* -Aporia" (unsaved)