pileup2seqz() requires sequenza (<= 2.1.2)

[HenrikBengtsson]

Issue

The new sequenza 3.0.0 does no longer implement Sequenza using Python. If used here, we'll get errors such as:

Error in system.file("exec", "sequenza-utils.py", package = "sequenza",  : 
  no file found

Tasks

1. Add assertion that we've got sequenza (<= 2.1.2) installed.

stopifnot(packageVersion("sequenza") <= "2.1.2")

2. Update aroma.seq to support sequenza (>= 3.0.0), which BTW, is a pain to install on our legacy TIPCC system, cf. https://github.com/HenrikBengtsson/Costello-PSCN-Seq/issues/24