Argument checks for makeLmer and makeGlmer

[pitakakariki]

Check that all arguments make sense, give helpful error messages if they don't.

e.g.

• NA's ir Poisson models because lambda is too big
• funny number of parameters if a predictor is constant (or predictors are rank deficient)
• fixef length when there are factors

[pitakakariki]

• Make sure the names in the VarCorr argument are used.
• Allow vector for VarCorr in place of a list.

[pitakakariki]

Add residual argument for residual variance, keep sigma for s.d. scale.

[pitakakariki]

e.g. https://github.com/lme4/lme4/issues/593