Fix multiple issues with the lyrics applet/engine

This fixes the following lyrics related issues:

-Amarok crashed when the lyrics applet was removed and re-added while a
track was playing and the user pressed "ESC".

-If no lyrics script was running cached lyrics were not displayed (but
an error message that no scripts are running instead - might be a
regression).

-If the user edited the lyrics in TagDialog the changes were not
"synchronized" to the lyrics applet (this is probably a regression).

REVIEW: 100892