larger avatar in the "in reply to" box

This one is for @BrentleyJones (cf.
http://meta.discourse.org/t/small-avatar-in-in-reply-to-box/8761)
added the "allow uploaded avatars" site setting
custom avatar support
generate avatars rake task
cleaned up non-used code
updated model annotations
updated locales
updated NGINX sample configuration
Merge pull request #1320 from ZogStriP/local-avatars

Local avatars
allow uploaded avatars by default
Fix typo in german translation
Merge pull request #1319 from adrianlang/patch-1

Fix typo in german translation
unbundled_require for gabbler
credit where it is due
FIX: avatars in quotes/oneboxes

Avatars in quotes/oneboxes are still pointing to the old
`/users/:username/avatar(/:size)` route.
So, this adds back the old avatar route for the transition period.
Merge pull request #1323 from ZogStriP/fix-avatars-in-quotes-in-already-cooked-posts

FIX: avatars in quotes/oneboxes
Add oneboxers for popular learning resources
FIX: N+1 query for avatars
Updated Dutch translation
Merge pull request #1326 from sanderdatema/dutch_translation

Updated Dutch translation