Load English messages from default theme.

Theme might not provide default English messages, and if it does, theme path
is the first to be searched during the import.
Date format setting was not used.
Merge pull request #300 from kotnik/dev

Misc fixes
updated changelog
first very basic integration test
first very basic integration test
don't leave the test site there
Fix #302 (with tests)
cheaper tests
correct naming
Fix Issue #298
added testcase for empty site
Fixed Issue #303 inconsistent breadcrumbs in gallery pages
unified crumbs between gallery and listings, added get_crumb into utils
flake8
flake8
flake8
run flake8 on travis
run flake8 on travis
booo! flake8 fails on py3 on travis :-(