Add emoji aliases for :) and :(

The suggestions can be confusing because : is the emoji prefix and the
parentheses match some emoji descriptions.

These aliases improve the UX because they will show up as the first
suggestions instead of some unrelated emojis.

Changelog: fixed

fixtures/emojis/aliases.json

 {
+   ":) ":"smile",
+   ":( ":"disappointed",
    "small_airplane":"airplane_small",
    "right_anger_bubble":"anger_right",
    "keycap_asterisk":"asterisk",