New `Try/Catch/EndTry` statements in Zencode

Blocks of Zencode in the When phase may include
```
Try
...
Catch error in 'e'
...
EndTry
```

Code in between may execute any When statement and setup the error messages / route them from what is returned in Zenroom. The exit status of Zenroom should stay set to `0` meaning success, since the error has been catched and handled consciously by the program.