The default value in the Metadata is saved in Bytes while the UI shows the size in MB.
Old code used the default in metadata as is, if database max size is unset the gui presents the default in bytes insted of MB which results in a huge number.
This commit fixes this by adding the calculation to transform the value to MB.

SpinBoxes for items with disabled checkbox should not be enabled.
If the user saves those settings as dissabled then reload the database the UI defaults to enable the SpinBox.
This commit fixes this by setting enable to false if the setting checkbox is not checked.

Values in DatabaseSettingsWidgetGeneral to convert from bytes to MB are written a more reabable way.