Re-use code of opening task details screen

This code is repeated at several places:
```java
                Intent viewTaskIntent = new Intent(Intent.ACTION_VIEW);
                viewTaskIntent.setData(mSelectedTaskUri);
                startActivity(viewTaskIntent);

```
Make it like this:
```java
        new BasicTaskDetailsUi(mSelectedTaskUri).show(this);
```

(Note: this comes out the #469 changeset)