Add translators to the credits dialog

- Add tooling at //tools/i18n to generate the file with the information
  about the translators: //src/json/i18n-credits.json.
- Change credits.json to remove an entry from a translator, who is now
  mentioned in the i18n credits.
- Change Makefile and release.bash to incorporate the i18n credit
  generation in the process of building the extension.
- Change options page to accommodate the translators section.

Change-Id: I7f3991f9c456c381832f4a7bebdfc5581ef9e4be
diff --git a/tools/i18n/blocked-users.txt b/tools/i18n/blocked-users.txt
new file mode 100644
index 0000000..52ad0a7
--- /dev/null
+++ b/tools/i18n/blocked-users.txt
@@ -0,0 +1,21 @@
+# These users were blocked because they are spammers, and therefore shouldn't be
+# included in the credits section.
+watabas
+p.karlsen
+Julpetter
+viki19822
+jjroot19
+mattiasxxpersson
+
+# These users joined the project but didn't make any translation, so they
+# shouldn't be credited neither.
+# NOTE: This list should be revisited in the future in case they actually
+# contribute.
+yolandarobinson3838
+ema168rutter
+bsiwanon
+nlmyst-35
+
+# This is the extension creator, so he shouldn't be credited as a translator
+# neither.
+avm99963