Adds `action=firstNew` parameter to unread conversation links in drop down

This way, the user can directly read the unread messages.
Clean up package
Merge branch 'refs/heads/master' into enhancement/cleanup

Conflicts:
	files/lib/data/conversation/ConversationAction.class.php
Removes obsolete imports
Makes use of DatabaseObjectList::$decoratorClassName
Merge pull request #51 from Gravatronics/enhancement/dboListObjectDecorator

Makes use of DatabaseObjectList::$decoratorClassName
Removes code that became obsolete with DBO::getObjectID()
Minor style improvements
Unified usage of the horizontal ellipsis character
Merge branch 'master' of github.com:WoltLab/com.woltlab.wcf.conversation
Merge pull request #46 from Gravatronics/enhancement/cleanup

Cleans up package
Merge pull request #52 from Gravatronics/enhancement/getObjectID

Removes code that became obsolete with DBO::getObjectID()
Makes use of "wcf.message.new"
Removes obsolete parameter
Sorts use statements
Another use statement sorting
Fixed embedded attachments and attachment permissions
Fixed permissions
Makes use of AbstractClipboardAction::execute()
Resets conversation count if user leaves conversation

Fixes #47