Add precision calo to electron chain

This MR foremost adds precision calo step to electron chains. I needed to make some dirty "fixes" to add empty steps in muons because of combined chains. - on my TODO to fix it soon. tagging @sshaw FI The construction of the complete selection step is now wrapped in SelectionCA which frees people from managing sequences themselves and improves readability. I have used configuration fragments from offline to setup cluster making & splitting (needed a small refactor there). @wlampl - can comment. Tagging @fernando to check PS. Sorry for trailing whitespace changes. I tend to forget not to do this cleanup automatically. Can be browsed ignoring whitespaces.