migrated to asciidoc including some content improvements

link to jpa reference added and links to solution zips corrected

links to artifacts corrected

build solutions zip files too

finalized exercise 2

ci_project_url corrected for correct link navigation

clarified docker-compose pull/build/up

build updated Helper docs

Using remote docker images to not need to build locally

preparations done for FS19

default expire artifacts after shorter time

- manually mark them to keep

reverted to older pandoc image

exercise solution fixes

rearranged exercises

prepared for U8

update of indexes and solutions

prepared week 4