Add uninstall stanza for TotalSpaces

Upon installation, two processes are started. One is resilient to the `:quit` directive, so I do believe this is the first usage of the `:signal` directive here. I tried using the `:signal` directive with only an `INT` signal, i.e.:

```
:signal    => ['INT', 'com.binaryage.totalspacescrashwatcher'],
```

but I got this error on uninstall:

```
Error: Cask 'totalspaces' definition is invalid: Each uninstall :signal must have 2 elements.
```

So, I added the `KILL` signal in an array, as shown in the example on the docs, and have the form seen in this PR, which works well enough.