Improve content and content group leaderboard

Improve duration pipe

Cut the duration string according to content duration.

a) If content duration is < 60 seconds, cut the minutes: ss.S

b) If content duration is > 60 seconds, cut the milliseconds: mm:ss

Improve participants content leaderboard

• Show duration cell only if content has duration
• Automatically hyphenate user aliases
• Use hash sign for position and center cell header and data
• Use timer icon instead of localized string for answer duration
• Stop using fixed width for cells
• Show score and current result points always among each other on mobile devices
• Show hint for current result points (answered partially correctly/correctly/incorrectly)
• Limit list to top ten entries but add column for own entry if not listed

Improve content group leaderboard

• Use table for displaying leaderboard
• Center entry position in fixed size cell
• Limit list to top ten entries but add column for own entry if not listed

Closes #1309 (closed), #1304 (closed), #1305 (closed)