Add Gettext PO files for all the languages.

Use Estonian as the base language, which is not the usual Gettext
way of doing things (English being the common default), but for
Scriba site it feels more correct to use Estonian as the base,
because it really is the base text.
Rename Gettext PO files with true locale codes.
Enable gettext localization in PHP.
Replace Makefile with Gruntfile.

Use the JavaScript Grunt tool for building.
Add setup instructions for Grunt in README.
Grunt task for compiling LESS stylesheets.

Plus a "debug" option to config.php to allow switching between
LESS files and generated CSS files.
Add default task to Gruntfile.

Compiles LESS and generates Gettext mo files.
Make shell commands apparent in README with '$'.
Add Grunt permissions task.

Remove related manual setup entry from README.
Add jshint task to Gruntfile.
Fix jshint reported problems.

- Indentation and trailing whitespace in Gruntfile.
- Unused variable in admin.js