Translatable strings for simplewallet

The system is mostly the Qt system, but we don't use Qt to avoid
the dependencies.

See README.i18n for details.

README.i18n

@@ -0,0 +1,45 @@
+The Monero command line tools can be translated in various languages.
+In order to use the same translation workflow as the future GUI, they
+use Qt Linguist translation files. However, to avoid the dependencies
+on Qt this normally implies, they use a custom loader to read those
+files at runtime. In order to update, or build translations files, you
+do need to have Qt tools installed, however. For translating, you need
+either the Qt Linguist GUI, or another tool that supports Qt ts files,
+such as Transifex. To run, you do not need anything Qt.
+
+To update ts files after changing source code:
+
+  ./utils/translations/update-translations.sh
+
+To add a new language, eg Spanish (ISO code es):
+
+  cp transations/monero.ts transations/monero_es.ts
+
+To edit translations for Spanish:
+
+  linguist translations/monero_es.ts
+
+To build translations after modiying them:
+
+  ./utils/translations/build-translations.sh
+
+To test a translation:
+
+  LANG=es ./build/release/bin/simplewallet
+
+To add new translatable sources in the source:
+
+  Use the tr(string) function if possible. If the code is in a class,
+  and this class doesn't already have a tr() static function, add one,
+  which uses a context named after what lupdate uses for the context,
+  usually the fully qualified class name (eg, cryptonote::simple_wallet).
+  If you need to use tr in code that's not in a class, you can use the
+  fully qualified version (eg, simple_wallet::tr) of the one matching
+  the context you want.
+  Use QT_TRANSLATE_NOOP(string) if you want to specify a context manually.
+
+If you're getting messages of the form:
+
+  Class 'cryptonote::simple_wallet' lacks Q_OBJECT macro
+
+all is fine, we don't actually need that here.