[backend] don't die if a package doesn't exists in preinstallimage generation
[webui] fix source file download link when not using anonymous mode.
[webui] proxy download requests for source files
[webui] make gravatar usage optional since it is a potential privacy issue.
[webui] take care about http proxy settings on host for using gravatar (untested)
[webui] fix http proxy support (thanks to the feedback from UkJung Kim)
[webui] options.yml rename for consistency: enable_gravatar -> use_gravatar
[webui] fine tune gravatar comment
[api] re-add the update package meta worker again, fixes migrations and api crashes due to invalid data
[api] add "rake updatepackagemeta" job to fix inconsitent package meta database
[backend] throttle long running pyblishing jobs
[backend] fix constraints BSXML entry for the 'flag' element
[api] fix status/bsrequest one place with db_project to project
      had been missing
[api] minor fix for db_project -> project model rename
[backend] also cache remote project binary info
[backend] put project config constraints in jobinfo
[backend] dispatch: merge project constraints with source constraints
[api] remove unused function package_create?
[api] fix one comparision in status/bsrequest
[api] add add_user and remove_user commands for atomar group modifications (with webui in mind)