patcher: patch groups (#812)

## Link to GitHub Issue or related Pull Request, if one exists
Fixes #245

## Description of change

Introduce patch groups. JSON schema now allows for a `"type": "group"`:

```json
    {
        "type": "group",
        "gameCode": "LDJ",
        "id": "timer-freeze",
        "name": "Timer Freeze Patches",
        "description": "Freezes various timers in the game."
    },
    {
        "name": "Standard/Menu Timer Freeze",
        "description": "Freezes all non-premium area timers.",
        "caution": "",
        "gameCode": "LDJ",
        "type": "memory",
        "group": "timer-freeze",
        "patches": [
            {
                "offset": 9962743,
                "dllName": "bm2dx.dll",
                "dataDisabled": "0F84",
                "dataEnabled": "90E9"
            }
        ]
    },
    {
        "name": "Premium Free Timer Freeze",
        "description": "Freezes all premium area timers.",
        "caution": "",
        "gameCode": "LDJ",
        "type": "memory",
        "group": "timer-freeze",
        "patches": [
            {
                "offset": 9111965,
                "dllName": "bm2dx.dll",
                "dataDisabled": "7E",
                "dataEnabled": "EB"
            }
        ]
    },
```

In the UI, these will show up as tree nodes. The parent is not actually
treated as a patch; e.g., its state is not saved to the patch manager
config file; only the child patches states are managed, the parent's
state only bubble up only in the UI.

In downlevel versions of spice, group parents will show up as a patch of
invalid type. Child patches will still show up as individual patches.

## Testing
*how was the code tested?*

src/spice2x/CMakeLists.txt

@@ -619,6 +619,7 @@ set(SOURCE_FILES ${SOURCE_FILES}
         patcher/config.cpp
         patcher/lifecycle.cpp
         patcher/loader.cpp
+        patcher/loader_group.cpp
         patcher/runtime.cpp
 
         # external