Add configuration options for script and style directories

To avoid the need to customize module source per site, I'm suggesting (and have included with this pull request) addition of configuration options for directory locations. I've been using this version on my own site for a while now and so far everything seems to work as intended :)

Other than that this PR includes converting couple of texts to translatable format and some very minor changes (fixed typo in one of comments, check that script / style files actually end with .js / .css etc.)