Install DokuWiki from official repository than bundling it.

* Administrator password is now generated
* DokuWiki is now easy to upgrade, just change $install_version in build
Merge pull request #4 from mfojtik/downloadable

Bug 1066438 - Upgrade DokuWiki by downloading it from official repository.
Updated README.md and fixed how password is printed to console.
Merge pull request #5 from mfojtik/readme_fix

Updated README.md and fixed how password is printed to console.