Image creation and downloading along with misc. fixes

- Add welder-web and cockpit-composer release instructions (bcl)

- Adjust image list layout to improve alignment (jgiardin)
- Fix blueprint packages getting added to history (jacobdkozol)
- Add a po-push target to the Makefile. (dshea)
- Don't call compose API on the blueprints page (lars)
- Support downloading images (lars)
- Fix issues with translated strings and add one more for "Close" (jgiardin)
- Make strings translatable (but includes build error) (jgiardin)
- Don't show custom sources section if empty (jgiardin)
- Add modal for listing sources (jgiardin)
- Include translations in the dist tarball (dshea)
- Update API calls error messages (jacobdkozol)
- Add loading images from prior sessions and sort by start time. (jacobdkozol)
- Don't update translations on every build (lars)
- Add a script for testing translations. (dshea)
- Make the editBlueprint selector more specific. (dshea)
- Add a i18n section to the README (dshea)
- Create cockpit translation modules. (dshea)
- Add translated messages. (dshea)
- Internationalize strings with react-intl. (dshea)
- Fix PR#309 imported issue. The rpm package should be welder-web*.noarch.rpm, not welder-web*.x86_64.rpm (henrywangxf)
- Images list UI refinements (jgiardin)
- cockpituous-release: Use upstream release-source (martinpitt)
- core: Use escalated privileges to access Lorax API (stefw)
- Submit coverage report only if present (atodorov)
- Fix created image not being added to state (jacobdkozol)
- blueprints: Show actual error message (lars)
- core: propagate errors from cockpitFetch() (lars)