Generalize 'kernels' and 'tower'.


git-svn-id: https://fricas.svn.sourceforge.net/svnroot/fricas/trunk@1561 b0c55286-4f34-0410-a049-a1e7e93b0762
re-establish HyperDoc content from .htex sources
add releaseNotes and "Changes to Spad" into ug15