Clean up Text releated IOTypes

[zepumph]

From phetsims/gravity-force-lab#183. We have RichTextIO and TextIO, and I see a few issues:

• Why do we need both of these, couldn't both be TextIO, and we can have one public interface for text in PhET-iO that all core types can adhere to?
• TextIO has many methods that I feel like are unneeded. These are about maxWidth and font options. Can we remove this?
• If we create a single TextIO type, we should make sure that the textProperty by default is phetioState:true.

Tagging @samreid and @chrisklus for comment.

[zepumph]

For the direct fix, I'm going to swap RichTextIO.textProperty to, by default, be phetioState: true.

[samreid]

It seems we could get pretty far by using one IO type for both of these. I don't understand all the public methods in RichText.js, but one day if we need to support them, we could make RichTextIO extends TextIO.

[zepumph]

• Why do we need both of these, couldn't both be TextIO, and we can have one public interface for text in PhET-iO that all core types can adhere to?

This is not the direction we have generally gone for IOTypes in the past 3 years. @samreid would you like a single IOType for Text? Or is it beneficial to split them out because then they match the core type? since Text's public API will not every be more than a subset of RichText, I don't care too much, and it is probably best as it is.

• TextIO has many methods that I feel like are unneeded. These are about maxWidth and font options. Can we remove this?

These have been removed

In general this issue is out dated. I'm ready to close. Please reopen if you feel differently @samreid.