Display behavior in text analysis tool

[craigsapp]

When clicking on the Modern letters option in the lyrics extraction pane:

The size of the pane will decrease temporarily as the old text is cleared out and before the new text is inserted. Instead, delete the old text just before adding in the next text to hopefully prevent the pane from temporarily resizing.

[craigsapp]

Implemented with issue 95c725b

Now when checking/unchecking the modernize text box, the text changes without an intermediate state of being empty while the other text format is being downloaded.