update copyright line, add author, fix remarks
update copyright line, fix authors
split support for R libraries into seperate modules
remove rextension.py module, replaced by rlibrary.py + dedicated easyblocks for R libs
fix use of make_R_install_option
rename RLibrary to RPackage, make RPackage support both installing as separate module and as extension
implement generic easyblock that supports installing extensions as actual extensions or as stand-alone modules
prepare for installing R packages by setting default class and filter
derive RPackage from ExtensionEasyblock and fix it for both scenarios