Add proper explanation to MR in archived projects

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Use humanize instead of titleize for MR title suggestion

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
 Merge branch 'improve-archived-projects' into 'master'

Proper message for archived projects at MR#show page

Fixes #940
Fix tests

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
 Merge branch 'humanize-over-titleize' into 'master'

Use humanize instead of titleize for MR title suggestion