tools/setup/emoji_dump/emoji_dump.py: Move bitmaps & *.ttx to var/.

Also update .gitignore to remove the old .gitignore markings for
these files' old locations.

.gitignore

@@ -23,8 +23,6 @@ static/js/bundle.js
 static/third/gemoji/
 static/third/zxcvbn/
 static/locale/language_options.json
-tools/setup/emoji_dump/bitmaps/
-tools/setup/emoji_dump/*.ttx
 tools/phantomjs
 node_modules
 npm-debug.log

tools/setup/emoji_dump/emoji_dump.py

@@ -11,15 +11,18 @@ from six import unichr
 
 from PIL import Image, ImageDraw, ImageFont
 
+ZULIP_PATH = os.path.join(os.path.dirname(os.path.abspath(__file__)), '../../../')
+
+EMOJI_DUMP_DIR_PATH = os.path.join(ZULIP_PATH, 'var', 'emoji_dump')
 
 class MissingGlyphError(Exception):
     pass
 
 
 def color_font(code_point, code_point_to_fname_map):
-    in_name = 'bitmaps/strike0/{}.png'.format(
+    in_name = os.path.join(EMOJI_DUMP_DIR_PATH, 'bitmaps/strike0/{}.png'.format(
         code_point_to_fname_map[int(code_point, 16)]
-    )
+    ))
     out_name = 'out/unicode/{}.png'.format(code_point)
     try:
         shutil.copyfile(in_name, out_name)
@@ -70,10 +73,13 @@ def main():
 
     # this is so we don't accidently leave ttx files from previous
     # runs of this script lying around
-    for fname in glob.glob("*ttx*"):
+    for fname in glob.glob(os.path.join(EMOJI_DUMP_DIR_PATH, "*ttx*")):
         os.remove(fname)
 
-    subprocess.call('ttx -v -z extfile NotoColorEmoji.ttf', shell=True)
+    # check if directory `var/emoji_dump` exists
+    subprocess.check_call(['mkdir', '-p', EMOJI_DUMP_DIR_PATH])
+
+    subprocess.call('ttx -v -z extfile -d {} NotoColorEmoji.ttf'.format(EMOJI_DUMP_DIR_PATH), shell=True)
 
     try:
         shutil.rmtree('out')
@@ -90,7 +96,7 @@ def main():
     emoji_map['red_car'] = emoji_map['oncoming_automobile']
 
     failed = False
-    code_point_to_fname_map = code_point_to_file_name_map("NotoColorEmoji.ttx")
+    code_point_to_fname_map = code_point_to_file_name_map(os.path.join(EMOJI_DUMP_DIR_PATH, "NotoColorEmoji.ttx"))
     for name, code_point in emoji_map.items():
         try:
             color_font(code_point, code_point_to_fname_map)