Text API Improvements

After some discussion in #263 we decided to rename `Message` to `Text` as it is used in many more places like player display names, signs or books and is not always used in terms of a "message".

We should also think about easier ways to construct messages, because using the message builder still requires a lot of code even for simple messages.

**TODO**:
- Fix and improve Javadocs to call it text now instead of message.
- Implement easier usable ways to construct messages, right now there is a lot of code required for this.