Add plurals

Adds the project `plurals-project` with a full set of appropriate data.

This updates the body for endpoints:

 - /projects
 - /source?ids=*
 - /trans/fr?ids=*
 - /source+trans/fr?ids=*

and adds endpoints:

 - /projects/p/plurals-project
 - /project/plurals-project
 - /projects/p/plurals-project/iterations/i/1
 - /project/plurals-project/version/1
 - /projects/p/plurals-project/iterations/i/1/r
 - /project/plurals-project/version/1/docs
 - /projects/p/plurals-project/iterations/i/1/r/plurals.txt
 - /project/plurals-project/version/1/doc/plurals.txt
 - /project/plurals-project/version/1/doc/plurals.txt/status/en-US
 - /project/plurals-project/version/1/doc/plurals.txt/status/fr
 - /project/plurals-project/version/1/locales
 - /source?ids=4567
 - /source?ids=4568
 - /source?ids=4569
 - /trans/fr?ids=4567
 - /trans/fr?ids=4569
 - /source+trans/fr?ids=4567
 - /source+trans/fr?ids=4568
 - /source+trans/fr?ids=4569
 - /stats/proj/plurals-project/iter/1/doc/plurals.txt
 - /stats/project/plurals-project/version/1/doc/plurals.txt/locale/en-US
 - /stats/project/plurals-project/version/1/doc/plurals.txt/locale/fr