Update and regenerate the bindings

Fixes #1 (closed)

It has been a long time since the bindings were last regenerated. Since then gir was constantly developed and got better at creating code so there are big changes. Pretty much everything changed. The submodules also changed. Because big changes were unavoidable, I took the liberty to align the structure of the repo with the recommended structure.

In order to make the review of this PR as easy as possible, I split it up in a bunch of smaller commits. Instead of looking at the diff, I suggest looking at the commits individually from oldest to most recent.

First the old code is deleted, then the folders and submodules are changed. Then the files to generate the bindings was changed, followed by generating the code. At the end, I also updated the README files.

The only manual implementations are a define in goa/goa-sys/tests/manual.h and two initialization macros in goa/lib.rs. Gir changed the name of the "getter" functions (e.g get_uri() -> uri()). There were also some changes in the automatically created goa/src/auto/manager.rs file. Since all methods were previously commented out, it should be an improvement.

I had to rename the automatically generated trait ObjectExt to GoaObjectExt to avoid a name conflict with glib::ObjectExt