[webconsole] add external CSS support (#1682)

Signed-off-by: R4SAS <r4sas@i2pmail.org>

contrib/i18n/README.md

@@ -0,0 +1,29 @@
+`xgettext` command for extracting translation
+===
+
+```
+xgettext --omit-header -ctr: -ktr -ktr:1,2 daemon/HTTPServer.cpp libi2pd_client/HTTPProxy.cpp
+```
+
+Regex for transforming gettext translations to our format:
+===
+
+```
+in:  msgid\ \"(.*)\"\nmsgid_plural\ \"(.*)\"\nmsgstr\[0\]\ \"(.*)\"\nmsgstr\[1\]\ \"(.*)\"\n(msgstr\[2\]\ \"(.*)\"\n)?(msgstr\[3\]\ \"(.*)\"\n)?(msgstr\[4\]\ \"(.*)\"\n)?(msgstr\[5\]\ \"(.*)\"\n)?
+out: #{"$2", {"$3", "$4", "$6", "$8", "$10"}},\n
+```
+
+```
+in:  msgid\ \"(.*)\"\nmsgstr\ \"(.*)\"\n
+out: {"$1", "$2"},\n
+```
+
+```
+in:  ^#[:.](.*)$\n
+out: <to empty line>
+```
+
+```
+in:  \n\n
+out: \n
+```