Create languages folder and .pot file with strings

Other changes, as per [Codex](http://codex.wordpress.org/Function_Reference/load_plugin_textdomain):
* load_plugin_textdomain should be called as early as 'plugins_loaded'
* path should use a trailing foward slash
* .pot filename should correspond to the domain ('job_manager', in this
case)

*Individual language files should be called, for instance for language pt_PT,  job_manager-pt_PT.po and job_manager-pt_PT.mo*