Disable tab to spaces converter in TextViewer

One problem is that this auto edit is not partition specific, it is applied on the whole document. At the moment this is only problematic for the multi line string partition, because when one presses tab there should be only one tab inserted, while in the default partition the cursor should indent to the same depth as of the previous line (the latter doesn't work anymore in the nightlies).

Another problem is that the linked mode model can't be applied to an auto edit strategy which means that we have to move away from them anyway (which I would like to do once when save actions and the the first version of IDE extensions are merged).