Show decoded payload if it is text with no new lines

https://github.com/aeternity/aepp-cli-js/blob/befbaaeb86755d56c52c066e75dede00390b449a/src/utils/print.js#L121

What we have now:
```
Payload            ba_Xfbg4g==
```
The actual payload is an empty string, which can be displayed as
```
Payload            ba_Xfbg4g== ("")
```