Fix "vswitch" plugin: undesired 'last' direction

[WShad]

Fixes wrong direction on "last" caused by changing workspace by external methods.
Example: switch workspace by activating window via wf-panel, as a result control_bindings_t knows nothing about this transition and remembers wrong "last direction".

[ammen99]

@WShad Thanks for looking into this issue! Is this the same as #1390 ?
If yes, I think an even better way of doing it will be to add a listener for the signal emitted when the current workspace changed. This way, we won't need to adapt any other plugins - simply vswitch will keep track of any workspace change and know how to revert that. Do you think this will work as well?