Add an "Import match list" tab to the scouting web page

This patch adds a new tab to the scouting web page to import the match
list. You have to point the server at a config file with `--tba_config`.
See its `--help` for more information.

Signed-off-by: Philipp Schrader <philipp.schrader@gmail.com>
Change-Id: I606915a6cc5776fe183da41ab8b04b063f57dafd
diff --git a/scouting/www/common.css b/scouting/www/common.css
new file mode 100644
index 0000000..35e943f
--- /dev/null
+++ b/scouting/www/common.css
@@ -0,0 +1,10 @@
+/* This CSS is shared between all scouting app tabs. */
+
+.error_message {
+  color: red;
+}
+.error_message:empty, .progress_message:empty {
+  /* TODO(phil): Figure out a way to make these take up no horizontal space.
+   * I.e. It would be nice to keep the error message and the progress message
+   * aligned when they are non-empty. */
+}