Decompose multi-arm trials

Based on the Moore-Penrose pseudo-inverse of the Laplacian (Rücker RSM 2012)
Multi-arm decomposition: refactor, test

Results are currently broken (not similar to regular consistency model)
Multi-arm trial decomposition: some experiments
Refactor for constrast-based and mixed models

 * Split ns into ns = ns.a + ns.r2 + ns.rm
 * Add $releffect$ to model template
 * Add template for relative effect likelihood
Handle input of data.re
Validate data.re requirements
Support relative-effect data in descriptives
guess.scale: take data.re into account
Working relative effect model
Mixed likelihood in working state