Editor : silently updated files on modification/deletion

When a file is modified/deleted outside of liteIDE, liteIDE displays a dialog for every single buffer currently opened in the IDE.

This is especially cumbersome when editing files under version control. `git stash` or `git checkout` tend to trigger an avalanche of dialog boxes inside the IDE.

This patch proposes the following modification the the IDE's behavior :
If a buffer is opened in the IDE, and the underlying file is modified/deleted
* if the buffer contains no unsaved modification, the buffer is silently updated/closed with the new content,
* otherwise, the previous behavior is preserved (ask for user input).