Show spaces horizontal bar

### Summary

This merge request adds a horizontal bar at top of room list, which shows spaces. By clicking on a space, user can filter out rooms belonging only to that specific space.

### Pending/ Help needed

#### Segfault when loading active connection on startup

Refer `void SortFilterRoomListModel::cacheSpaceHierarchy()` ([link](8c372800d7 (b969e462c30df43ef3714ea441948d8d8027f6a0_117_126))) in `src/sortfilterroomlistmodel.cpp`.

On [line 129](8c372800d7 (b969e462c30df43ef3714ea441948d8d8027f6a0_117_129)), I have called `connection->allRooms()`, which segfaults if the active connection hasn't been loaded yet. Is there a way to ensure that `Controller::instance().activeConnection()` on line 128 waits till connection is loaded?

#### Avatars

Avatars on space horizontal bar aren't aligned to vertical middle. I'll need help with that. 

Using the code below doesn't help with padding

```qml
delegate: QQC2.Control {
    topPadding: 10
    contentItem: Kirigami.Avatar { ..... }
}
```

This complains about uninitialized properties in `Kirigami.Avatar`. (`id`, `currentRoom`, `avatar`, `index` are properties utilized during run time)

After we get around these two issue, this MR will be ready from my side.

src/spacehierarchycache.cpp

@@ -0,0 +1,72 @@
+// SPDX-FileCopyrightText: 2022 Snehit Sah <hi@snehit.dev>
+// SPDX-License-Identifier: LGPL-2.1-only OR LGPL-3.0-only OR LicenseRef-KDE-Accepted-LGPL
+
+#include "spacehierarchycache.h"
+
+#include "controller.h"
+#ifdef QUOTIENT_07
+#include "csapi/space_hierarchy.h"
+#endif
+#include "neochatroom.h"
+
+SpaceHierarchyCache::SpaceHierarchyCache(QObject *parent)
+    : QObject{parent}
+{
+    cacheSpaceHierarchy();
+    connect(&Controller::instance(), &Controller::activeConnectionChanged, this, [this]() {
+        cacheSpaceHierarchy();
+    });
+}
+
+void SpaceHierarchyCache::cacheSpaceHierarchy()
+{
+#ifdef QUOTIENT_07
+    auto connection = Controller::instance().activeConnection();
+    if (!connection) {
+        return;
+    }
+
+    const auto roomList = connection->allRooms();
+    for (const auto &room : roomList) {
+        const auto neoChatRoom = static_cast<NeoChatRoom *>(room);
+        if (neoChatRoom->isSpace()) {
+            populateSpaceHierarchy(neoChatRoom->id());
+        } else {
+            connect(neoChatRoom, &Room::baseStateLoaded, neoChatRoom, [this, neoChatRoom]() {
+                if (neoChatRoom->isSpace()) {
+                    populateSpaceHierarchy(neoChatRoom->id());
+                }
+            });
+        }
+    }
+#endif
+}
+
+void SpaceHierarchyCache::populateSpaceHierarchy(const QString &spaceId)
+{
+    auto connection = Controller::instance().activeConnection();
+    if (!connection) {
+        return;
+    }
+#ifdef QUOTIENT_07
+    GetSpaceHierarchyJob *job = connection->callApi<GetSpaceHierarchyJob>(spaceId);
+
+    connect(job, &BaseJob::success, this, [this, job, spaceId]() {
+        const auto rooms = job->rooms();
+        QVector<QString> roomList;
+        for (unsigned long i = 0; i < rooms.size(); ++i) {
+            roomList.push_back(rooms.at(i).roomId);
+        }
+        m_spaceHierarchy.insert(spaceId, roomList);
+        Q_EMIT spaceHierarchyChanged();
+    });
+#endif
+}
+
+QVector<QString> SpaceHierarchyCache::getRoomListForSpace(const QString &spaceId, bool updateCache)
+{
+    if (updateCache) {
+        populateSpaceHierarchy(spaceId);
+    }
+    return m_spaceHierarchy[spaceId];
+}