Improve UI for mass-file reformatting a little

Summary:

• consistent usage of "Reformat"
• use "..." in action text to indicate dialog coming up
• in dialog use "Reformat/Cancel" instead of "Yes/No", result more obvious

Reviewers: KDevelop, brauch

Reviewed By: KDevelop, brauch

Subscribers: brauch, kdevelop-devel

Differential Revision: https://phabricator.kde.org/D6967