BIM: Covering objects should support additions and subtractions

### Problem description

Currently Covering objects cannot have other BIM objects added or subtracted to/from them. During the development cycle, and to reduce complexity, the `applyShape` and `processSubShapes` functions from the parent ArchComponent were shortcircuited. In practical terms, these need to be called to be able to use the feature.

### Workbench affected?

BIM

### Steps to reproduce

1. Double-click on a Covering object to edit it

### Expected behavior

The edit task panel shows the Components task box to add or remove components

### Actual behavior

The edit task panel does NOT show the Components task box to add or remove components

### Development version About Info (in Safe Mode)

```shell
1.2.0dev (merged today, not yet in a weekly build)
```

### Last known good version (optional)

```shell

```