Activity Report print fixes

[notmart]

We are using Charm and Activity report (printing as PDF) internally in the company and had several issues with it:

• The user name disappeared from the report for several users, it seems a problem of the user name copy to and from the metadata, where sometimes it went blank. Now it checks explicitly for blank values in that cache
• The activity report header had wrong dates printed, as I do a report for "Last Month", the result says 1st May - 1st June, instead of 1st May - 31st May. Now the correct range appears
• In the final PDF, the <Previous Month><Next Month> links are visible, which make the printout look quite broken. Now the next/previous function is in outside pushbuttons