Editor rephrased dialogs

Following my [previous pull request](https://github.com/visualfc/liteide/pull/143) :

This patch rephrases the dialogs when asking if unsaved modifications should be discarded.

* Both dialogs now ask a "Yes"/"No" answer,
* answering "Yes" will discard the unsaved modifications and reload the file/close the editor (when the file is modified/deleted),
* answering "No" will keep the editor open with the unsaved modifications.