Release Version 0.2.4

Fix virtualbox_install() function during boot when online version
doesn't exist or is not checked - missing local filename.
Added $VBOX_PKG_LOCAL_FILENAME and $VBOX_PKG_LOCAL_FILENAME parameters -
includes path to file.

Removed remark from plugin upgrade button
Merge pull request #6 from theone11/testing

Release Version 0.2.4