Add more document metadata

[kalitine]

Current Behavior
Any document is composed of

• a title
• a content
• a key (document unique identifier for sharing)

Only the content is managed by the universal JavaScript API mute-core. Indeed for example when the document is shared between 2 peers, its content is synchronized by mute-core, the key is shared manually (as a part of the URL), but its title is not synchronized (see issue #55 )

Also in MUTE only (not bot-storage) we are able to see the document location (Either Browser Database: local/trash folders, or Bot Storage).

Expected behavior
Having more document metadata which are synchronized by mute-core, add some others that proper to MUTE. Among them:

• Managed by mute-core
  • title
  • key (useful for bot-storage)
  • Creation date/time
  • Owner (for example the pseudonym of the peer who created the document)
• Proper to MUTE
  • Opened data/time
  • Modified data/time
  • Location
  • Size

[kalitine]

Following are added:

• title
• creation date
• cryptographic key