Alternative small widgets.
Some alternatives to the default widgets, and some additional ones too.

List of widgets provided:

- Playback Buttons (Alt):
Playback buttons and more with tooltips and state.
Buttons will be disabled depending on the state that the button controls.
This widget is unfortunately not configurable at the current time.

- Volume Scale:
Volume selector by a scale widget.
Right-click to select either a linear, cubic or dB scale,
similar to the official volume widget.
Configuration keys: scale: str, step1: float, step2: float, width: int, height: int.

- DSP Combo:
Selecting a saved DSP preset.
Configuration keys: maxwidth: int.

- Button (Alt):
Provides a button using an icon based on gtk_image_new_from_icon_name.
gtk-icon-browser usually provides a way to see a list of icons together with
their name, but a GTK theme can also provide additional ones.
The label allows for title formatting and will update depending on deadbeef
message event IDs if specified. See deadbeef.h:DB_EV_* for a list of them.
The action is identified by the deadbeef action names.
A list of the default deadbeef actions can be found in deadbeef/src/coreplugin.c:action_*
Plugins are also able to provide additional actions.
deadbeef.h:DB_plugin_action_t::name is what to look for.
Configuration keys: action: str, iconname: str, label: str, eventupdates: list[uint].

- Title Formatting Tester:
Displays the title formatted string based on track selection.
Useful for testing and formatting track metadata.
Configuration keys: input: str.

- Queue View:
Displays a list of play items that currently are in the play queue.
Play items in the queue can be removed by either Right-click > Unqueue
or by selecting and pressing the Delete key.
It is currently very bare-bones and lack a lot of other useful features.
Configuration keys: title: list[str], format: list[str], width: list[uint].

- Output Plugin Combo:
Selecting an output plugin.
Configuration keys: maxwidth: int.

- Output Device Combo:
Selecting an output device of the output plugin.
Configuration keys: maxwidth: int.

- Popover Toggle (GTK3):
A button which displays a popover containing a widget when pressed.
Configuration keys: width: int, height: int, iconname: str, label: str, tooltip: str, padding: uint.

- Config Toggle Button:
Provides a toggle button, similar to "Button (Alt)", but also being able to
switch between two values in the config.
If action is specified, then the toggle button will execute the action instead
of modifying the config directly, meaning that it would only read from the
config to check the toggle state.
Configuration keys: action: str, iconname0: str, iconname1: str, label0: str, label1: str, tooltip0: str, tooltip1: str, configvalue0: str, configvalue1: str, configkey: str, cssclasses: str.