[BUG] default predicted slot for tSNE is set to a slot that doesnt exist

example:
```r
M = tSNE()
predicted(M)
```

result:
`"tnse"`

this causes tSNE when part of a sequence to fail because
```r
predicted(M)
```
```
Error in slot(obj, name) : 
  no slot of name "tsne" for this object of class "tSNE"
```

To work around this the predicted slot can be set when creating the object:
```r
M = tSNE(predicted = 'Y')
```

