A set of requirements for the SysApps security model.

This is not the 'security model' itself, but some requirements that a
security model should aim to solve.

This work is based on source data from the webinos project, the sysapps
mailing list, varios B2G pages and mailing lists, plus academic literature.
Security Requirements: minor rephrasing and clarification of user requirements.

Minor edit only.
Security Requirements: minor typo fix.

Typo in the 'File API' section.
Security model: fixed numbering and a missing clause in communication.
Security model: minor edit to references
Typos and minor changes to the security model requirements document.

Changes based on Janusz Majnert's email
Merge remote-tracking branch 'oldrepo2/master' into add-security-model-proposal
Copied security requirements from old repository
Merge pull request #1 from jplyle/add-security-model-proposal

Add security requirement document.