Re-factor the avatar system and support avatar uploads

The user is now able to upload an avatar, and pick one in a list.

This functionality should eventually be abstracted in a community
package but we still need to work on a great public API. We rely on
collectionFS to manage uploaded avatars. We also removed
bengott:avatar which was trying to solve the wrong problem (namely
displaying the avatar, which is as simple as displaying an image), and
not a avatar system as it should be.

Gravatar support is coming (back) soon. We may also want to have a
list of default fun avatars the user can choose instead of uploading
its own one.

client/components/sidebar/sidebar.jade

@@ -27,11 +27,7 @@ template(name="membersWidget")
       | {{_ 'members'}}
     .board-widget-content
       each currentBoard.members
-        +userAvatar(
-          userId=this.userId
-          draggable=true
-          size="small"
-          showStatus=true)
+        +userAvatar(userId=this.userId showStatus=true)
       unless isSandstorm
         if currentUser.isBoardAdmin
           a.member.add-member.js-manage-board-members
@@ -86,7 +82,7 @@ template(name="addMemberPopup")
     +esEach(index="users")
       li.item.js-member-item(class="{{#if isBoardMember }}disabled{{/if}}")
         a.name.js-select-member(title="{{ profile.name }} ({{ username }})")
-          +userAvatar(user=this size="small")
+          +userAvatar(userId=_id)
           span.full-name
             = profile.name
             | (<span class="username">{{ username }}</span>)

client/components/sidebar/sidebarFilters.jade

@@ -23,7 +23,7 @@ template(name="filterSidebar")
           with getUser userId
             li(class="{{#if Filter.members.isSelected _id}}active{{/if}}")
               a.name.js-toogle-member-filter
-                +userAvatar(user=this size="small")
+                +userAvatar(userId=this._id)
                 span.sidebar-list-item-description
                   = profile.name
                   | (<span class="username">{{ username }}</span>)