Miscellaneous server interface enhancements

[kristian-lange]

• Statistics should be on an independent tab (with info, jobs, participants), not in participants. So we could order the tabs like this: INFO / JOBS / PARTICIPANTS / STATISTICS
• Downloading data button should be with other buttons and it should always be in csv format (there is no need for the other options or the cached version, this is never used).
• Buttons would therefore be: Experiment / Job / Data / Archive / Delete / Sharing
• The manage participants Button of the participants tab should be at the top of the panel, not the bottom.
• Activate/Stop jobs for a participant: when the jobs are set to finished it is impossible to set them back to pending. A button to do that would be useful…
• Buttons to clear participant_data, session_data, study_data. Right now we use a custom OS program to do that when needed.