Added reminder to make tabs save on closing
Implemented saving on tab close, but introduced bug which means fileName
is transferred between tabs
Fixed tab name transferring on close
Began work on fixing closing empty tabs
If note has been changed and not saved, when the tab is closed the user
will be prompted to save
Added visual changed indicator. Needs implementation.
Added change indicator functionality
Added functionality to title and subtitle buttons
Implemented "make note-level" button and neatened up makeLevel()
function