gdu-block-row: Minor tweaks to the "Confirm Check" confirmation dialog
The "Confirm Check" title isn't phrased as a direct question. Also, the "Ok" button isn't capitalized correctly and it isn't a standard term to use on this button.
To fix this, rename the confirmation dialog to "Check Filesystem?" and the "Ok" button to "Start Check" (and add a mnemonic to this button)
Closes #371 (closed)
/cc @cyberphantom52