Show achievements badges on talks

[fcamblor]

It would be very nice to show some special achievement badges at different places in the app :

• On feedback screen :

• On Talk Details screeen
• On schedule (once the talk has been performed)

Badges I would think about :

• Daily + Overall average votes : Top 10 / Top 5 / Top 3 / Top 1
• Daily + Overall XXX Bingo ratio (for example: highest "this was fun!" ratio) : Top 5 / Top 3 / Top 1
• Daily + Overall number of votes : Top 5 / Top 3 / Top 1

[fcamblor]

We should have variations of these badges :

• Big badges (64x64 or 96x96) displayed on the feedbacks screen & talk details screen
• Small badges (16x16) displayed on schedule (for people wanting to browse best-rated talks)

(for XXX Bingo ratio entries, we might think about writing small text representing the entry in SVG, above a badge template picture)

Given that we're only showing "best" talks, we should make this information public, so that speaker can share this information, for example when they submit their talk on CFPs and they need some previous talks references

[fcamblor]

Requires #71 to be implemented first