HaikuDepot: change window frame setting.

* Moved entirely into MainWindow.
* Moved duplicated code into separate methods.
* Resize the main window on larger screens by default, as we can make
use of the extra space.
* Use BWindow::MoveOnScreen() instead of make_sure_frame_is_on_screen()
as the former has more info. And is even smarter now as it can
optionally resize windows to fit on screen.
* Center window on screen by default (ie. when there are no settings).

HaikuDepot: Centralized user account features in the UI

There is now a right-aligned second menu bar for the account management.
The menu label is what was previously shown underneath the search terms field.
The menu items have moved from the Tools menu into the new user menu. This
means the login/logout functionality is directly available where the login
info is shown in the UI when you click it.

HaikuDepot: Split generic and specific UI classes

* Also fixed placement of PackageManager which I must have
dropped into the wrong folder by accident.

HaikuDepot: change window frame setting.

* Moved entirely into MainWindow.
* Moved duplicated code into separate methods.
* Resize the main window on larger screens by default, as we can make
use of the extra space.
* Use BWindow::MoveOnScreen() instead of make_sure_frame_is_on_screen()
as the former has more info. And is even smarter now as it can
optionally resize windows to fit on screen.
* Center window on screen by default (ie. when there are no settings).

HaikuDepot: Centralized user account features in the UI

There is now a right-aligned second menu bar for the account management.
The menu label is what was previously shown underneath the search terms field.
The menu items have moved from the Tools menu into the new user menu. This
means the login/logout functionality is directly available where the login
info is shown in the UI when you click it.

HaikuDepot: Split generic and specific UI classes

* Also fixed placement of PackageManager which I must have
dropped into the wrong folder by accident.