Now text speed options for 2-click Context-sensitive SettingsBar
component are configured as properties of itself instead of relying on
Popochiu and PopochiuSettings.

- [fea] Add `is_playing_cue` function to AudioManager so one can now if
  a PopochiuAudioCue is playing.
- [fea] When a PopochiuCharacter stops speaking, its voice stops too if
  it is still playing. For this to work properly, the PopochiuAudioCue
  should not be marked as `can_play_simultaneous`.
- [upd] Now moving the GUI to "res://game/graphic_interface" takes into
  accound if a script is a tool so it adds the @tool annotation to the
  target file.
- [upd] Room tab selects the scene of created Markers in the FileSystem
  when clicking the Marker row.