Display used package versions in interface

[tomsmeding]

The playground currently makes a number of packages available to code the user submits (list here, see also #11).

However, the user may want to know the versions of the packages being used; this should be made available in the UI. Probably by letting mkbuildscript.sh write a freeze file as well and parsing that; not sure what the UI element should look like, perhaps some "about" page/modal (suggestion by @Kleidukos)