Filter emoji where "visible_in_picker" is set to false. (#907)

Addresses #770

app/src/main/java/com/keylesspalace/tusky/entity/Emoji.kt

@@ -16,10 +16,12 @@
 package com.keylesspalace.tusky.entity
 
 import android.os.Parcelable
+import com.google.gson.annotations.SerializedName
 import kotlinx.android.parcel.Parcelize
 
 @Parcelize
 data class Emoji(
         val shortcode: String,
-        val url: String
+        val url: String,
+        @SerializedName("visible_in_picker") val visibleInPicker: Boolean?
 ) : Parcelable