Added internationaliztion capabilities to OpenDSA.
Used the 'lang' variable in the configuration file to set up the book language.
A list of languages supported by sphinx can be found at http://sphinx-doc.org/config.html#confval-language.
Created a translation JSON file 'language_msg.json' in the 'tools' directory.
Each language is represented by its code in language_msg.json.
The terms for each language are grouped in two categories:
-"jinja" for the terms that will be added inside the configuration
file. They will be passed by Sphinx to the templating system (jinja + haiku).
-"js" for the terms processed by odsaMOD.js library and injected while the
page is loading.
Structure of language_msg.json:
{
  "en"{
    "jinja": {
      "term1": "en_term1",
      ...
    },
    "js": {
      "term2": "en_term2",
      ...
    }
  },
  "fi"{
    "jinja": {
      "term1": "fi_term1",
      ...
    },
    "js": {
      "term2": "fi_term2",
      ...
    }
  },

Updated the configuration process to read the language variable.
If a translation for the entered language is not available, the default
language english is used. The configuration process inserts the language
inside the onfiguration file and copies the translation file in the
Book _static directory.

Avembed directive has been updated to display show/hide butons caption
in the right language.
Translation file contains only english and french languages so far.
Merge branch 'master' of ssh://github.com/OpenDSA/OpenDSA