Manufactored solutions and general validation/verification

[pschlatt1]

We should think of a good quantitiative way of validate/verify Neko, i.e. a good library of MMS cases and/or physical cases with known solutions (Kovasznay flow (https://www2.karlin.mff.cuni.cz/~prusv/vyuka/2016-2017/zs/downloads/kovasznay.pdf), TS waves, generalised Taylor-Green (eddy example)).

Some of these cases could certainly be formulated as Master's thesis projects.