Debugger: Reorganize settings classes.

- Refactor TeamUiSettingsFactory into an abstract base class with implementing
subclass DebuggerUiSettingsFactory.
- Adjust SettingsManager to expect the UiSettingsFactory to be passed in as an
initialization parameter, and refactor accordingly.
- Move GuiTeamUiSettings.* into a user_interface/gui subfolder.

No functional change, simply reorganization towards splitting the debugger's
core functionality into a separate library from the application to aid in
sharing with remote_debug_server.