refactor emoji code into package

1) EmojiTextView and EmojiEditText are used instead of
   using code to emojify text.

2) Emoji categories' code points are specified in XML

3) EmojiDrawer itself is a fragment, and its pages are
   also fragments, allowing for better memory
   management.

Fixes #2938
Fixes #2936
Closes #3153

// FREEBIE

src/org/thoughtcrime/securesms/components/emoji/StaticEmojiPageModel.java

@@ -0,0 +1,24 @@
+package org.thoughtcrime.securesms.components.emoji;
+
+import android.support.annotation.DrawableRes;
+import android.support.annotation.NonNull;
+
+public class StaticEmojiPageModel implements EmojiPageModel {
+  @DrawableRes private final int   icon;
+  @NonNull     private final int[] codePoints;
+
+  public StaticEmojiPageModel(@DrawableRes int icon, @NonNull int[] codePoints) {
+    this.icon       = icon;
+    this.codePoints = codePoints;
+  }
+
+  public int getIconRes() {
+    return icon;
+  }
+
+  @NonNull public int[] getCodePoints() {
+    return codePoints;
+  }
+
+  @Override public void onCodePointSelected(int codePoint) { }
+}