add command to summarize space usage

[icewind1991]

Helps with figuring out what is taking up the space or debugging quota issues.

example output:

files: 9.6 MB
- src: 8.6 MB
  - private: 4.1 MB
    - Files: 952 KB
      - Storage: 219 KB
        - Wrapper: 104 KB
      - Cache: 196 KB
      - ObjectStore: 95 KB
      - Node: 72 KB
    - DB: 243 KB
      - QueryBuilder: 120 KB
    - AppFramework: 238 KB
    - Share20: 221 KB
    - legacy: 205 KB
    - Authentication: 186 KB
    - User: 127 KB
    - Repair: 111 KB
    - Collaboration: 107 KB
    - Security: 107 KB
    - Preview: 98 KB
    - App: 87 KB
  - l10n: 2.5 MB
  - public: 1.5 MB
  - composer: 424 KB
- picture.png: 960 KB

[blizzz]

I am not merging due to an open question ^

[icewind1991]

/backport to stable25

[icewind1991]

/backport to stable26