First attempt for fixing the scroll jump and cursor move.

Basically I've done this:

• revert of fileDeleted/delItem functions removal
• introducing of _pendingVfiles (they are meant to be used only when refreshing)
• created vfs::storeAndEmitUpdates(...) method for determining actual changes between _vfiles and _pendingVfiles and emitting selective change signals (add/update/delete)
  • this function is kind of stolen from vfs::vfs_refresh() of master branch
• off-topic change: vfs::clear(vfileDict vfiles) -> vfs::clear(vfileDict &vfiles) to actually clear the hashmap keys