The pattern to construct `Application` was to use the `try_create`
method from the `C_OBJECT` macro. While being safe from an OOM
perspective, this method doesn't propagate errors from the constructor.
This patch make `Application` use the `C_OBJECT_ABSTRACT` and manually
define a `create` method that can bubble up errors from the
construction stage.
This commit also removes the ability to use `argc` and `argv` to
create an `Application`, only `Main`'s `Arguments` can be used.
From a user point of view, the patch renames `try_create` => `create`,
hence the huge number of modified files.
Rip that bandaid off!
This does the following, in one big, awkward jump:
- Replace all uses of `set_main_widget<Foo>()` with the `try` version.
- Remove `set_main_widget<Foo>()`.
- Rename the `try` version to just be `set_main_widget` because it's now
the only one.
The majority of places that call `set_main_widget<Foo>()` are inside
constructors, so this unfortunately gives us a big batch of new
`release_value_but_fixme_should_propagate_errors()` calls.
Similar to the Settings application, this adds a single Screensaver
application to launch all screensaver demos. This is to declutter the
taskbar menu a bit.
