Improve/update wiki documentation

[kouralex]

At the moment the wiki pages are out-of-date (both with respect to new features of Skosmos 2.x and some information on Skosmos 1.x related quirks to be removed).

We should align the wiki pages with fresh eyes, e.g.,

• [ ] All configuration related stuff should reside in one page: @joelit

  1) plug-ins (introduce example plug-ins developed for Finto service) 2) vocabulary configurations 3) CSS files 4) translations

• [ ] Packaging wiki page: @kouralex

  1) Currently supported options Virtual machine Vagrant, docker 2) Not recommended Windows-installation (gettext issues)

• [x] Add documentation for Continuous Integration services currently in use, in detail. @kouralex

• [ ] Separate support and development wiki page @joelit

  mention Skosmos-users list Licenses (no) support contract Development model - including testing

• [ ] update Skosmos.org where necessary @kouralex

• [x] roadmap wiki page @osma

[osma]

More specific: #708 (usePlugin docs missing)

[osma]

I created a simple roadmap wiki page: https://github.com/NatLibFi/Skosmos/wiki/Roadmap It's more about the process than concrete goals, since we haven't set them yet.