Corrected eraseDone() message. Added additional dialog box to better
inform the user.
Minor adjustment to text. Updated TODO to make it clearer that it's
unlikely we'll be able to tell a priori how much time an erase operation
will take.
Merge pull request #211 from TauLabs/kenz/gcs_erase_NVRAM_dialog

Corrected eraseDone() message. Added additional dialog box to better inform the user.