Key events should be delivered when control.[trash|line|etc] are false

Nobody has claimed this yet.

I am trying to make my own draw control modes/behaviors and it seems as though events.js consumes the delete/backspace/ keys if control.trash is set to false. If trash is false, I cannot get the key event to do my own thing with it. Unfortunately, when trash is true, a trash can button is placed on the map - which i don't want.

It does this for the the controls for line, point, and polygon too. If the controls are false, the event should be delivered for handling by the mode

In at least the keydown, it seems like
```
else if (isKeyModeValid(event.keyCode)) {
currentMode.keydown(event);
}
```
should be removed and
```
else { currentMode.keydown(event);}
```
should be added at the end. Full code attached below

```
// 8 - Backspace
// 46 - Delete
events.keydown = function(event) {
if ((event.srcElement || event.target).classList[0] !== 'mapboxgl-canvas') return; // we only handle events on the map

if ((event.keyCode === 8 || event.keyCode === 46) && ctx.options.controls.trash) {
event.preventDefault();
currentMode.trash();
} else if (isKeyModeValid(event.keyCode)) {
currentMode.keydown(event);
} else if (event.keyCode === 49 && ctx.options.controls.point) {
changeMode(Constants.modes.DRAW_POINT);
} else if (event.keyCode === 50 && ctx.options.controls.line_string) {
changeMode(Constants.modes.DRAW_LINE_STRING);
} else if (event.keyCode === 51 && ctx.options.controls.polygon) {
changeMode(Constants.modes.DRAW_POLYGON);
}
};

events.keyup = function(event) {
if (isKeyModeValid(event.keyCode)) {
currentMode.keyup(event);
}
};
```

Start in events.js, especially keydown and keyup handling for trash, line_string, point, and polygon controls. Verify how disabled controls affect delivery to currentMode, then confirm that delete, backspace, and other mode keys reach the mode when the corresponding control is false, without adding its map button.

Written by the indexing model from the issue text.