Fix back button issue in the import lyric screen

[andy840119]

What's fixed in this PR:

• Remove the back button because it will hide the lyric editor.
• Should exit import screen only if in the drag screen(first import lyric step)
• Add abort import feature in the import manager.
• Checking able to roll-back to the target page instead of checking current page if user click the back button.

[andy840119]

Also, there's something found but not fixed in this PR(might create another issue for it):

• Should be better to press Esc to go-back to previous screen.
• Should think about should show the popover if change the step by fixing invalid part by lyric maker.