Changed 'paste' to 'put in clipboard' in the queue

Just using 'paste' in the context menu is not very clear. It even
is the opposite of what actually does. This change makes it a bit
more clear to the user what the thing actually is about..

In order to do this I've added it the messages file under the key
'queue.context_menu.put_in_clipboard'.

This also resolves #38.
Added a UI thread check to the SWT clipboard service

I've added a check to the SWT clipboard service to see if calling
thread is the UI thread. If it is it will simply run the SWT
methods from the current thread. If not it will do it on the UI
thread. Because there is only one UI thread it can only execute one
thing at a time. This caused a deadlock because the SWT thread
was waiting on itself to finish.
The SWT queue now uses the setContent command instead requestSet

The latter is deprecated and setContent should be used instead.
Made the queue columns translatable
Moved the queue window title to the messages file and renamed it to 'queue'
Added some comments to the SWT queue code
Update messages.properties

'queue.column.data=Data'
'queue.column.date=Data'

Changed in 

'queue.column.data=Content'
'queue.column.data=Content'
Merge pull request #40 from MMS-Projects/feature/queue-improvements

Improved the SWT queue a bit