Updated main layout so that all types of flash messages are displayed, and
updated sessions controller so that login errors result in only one flash
message and login successes are displayed as such.

Resolves Redmine issue #2509.
Merge branch 'master' into BulkUpload1920

Conflicts:
	app/views/layouts/application.html.erb
Changed location of some bulk_upload fixture files and modified tests accordingly.
Major overhaul to bulk_upload code: Use exceptions to handle and store
information about validation errors.
Only store citation list in session if needed.
Fixed typos.