talkatu/talkatu

Disable the old TextBuffer serialization formats for the time being.

We'll come back and port these to Gdk.ContentSerializeFunc's after we get
everything else working.

Testing Done:
Compiled and verified the warnings were gone.

Reviewed at https://reviews.imfreedom.org/r/1267/
# Building
Talkatu uses [meson](https://mesonbuild.com) as it's build system.
Meson requires you to build in a directory other than the source directory.
To compile you can use the following commands:
```
meson build
cd build
ninja install
```