Add experimental feature to translate links

This CL adds support for translating links directly from the context
menu. This support is experimental, since many details of the
implementation might change after testing it for a while and finding
ways to improve it (hopefully also thanks to the feedback given by folks
who might also test this).

For this reason, the feature is only enabled in Canary builds of the
extension for now (or when the extension is being developed).

This CL also changes the Crowdin configuration file so strings that
change in the source file and are uploaded for translation don't remove
the existing translations. This is because although no strings are
changed in this CL, the description/context of 2 strings has changed,
and this is to be sure that the translations are not erased.

Bug: translateselectedtext:7
Change-Id: I862af18eee8830c901e7fe7d2b473cab43d9bbe7
diff --git a/tools/i18n/crowdin.template.yml b/tools/i18n/crowdin.template.yml
index 9186c2a..17aba16 100644
--- a/tools/i18n/crowdin.template.yml
+++ b/tools/i18n/crowdin.template.yml
@@ -35,5 +35,8 @@
       "zh-TW" : "zh_TW",
     }
   },
+
+  # This is so when editing a source string, the translations are preserved.
+  "update_option": "update_without_changes",
  }
 ]