Supporting "all versions" in AffectedPackage

[Hritik14]

In the new model #500 time travel is required to be implemented at a different time than import. This means versions values like "all" need to be stored. Currently, AffectedPackage uses univers's VersionSpecifier which does not support an open range as "all" (and it is for good).
Maybe we can use a customscheme named all for this purpose.

Here's one entry from nginx for our future hall of shame:

An error log data are not sanitized
Severity: none
CVE-2009-4487
Not vulnerable: none

located at: http://nginx.org/en/security_advisories.html

[pombredanne]

See #525

[Hritik14]

vers now supports * range ie vers:ANY/*.