Add model summary info tab to shinyMer

[carlbfrederick]

I find myself just almost exclusively exploring my merMods with shinyMer() ... perhaps the shinyMer landing page should be some model info including perhaps

• summary of random effects (var/covariance matrix) for each level
• fixed coefficients (personally I am ambivalent about this)
• total variance
• optimization parameters (reml vs ml; #adaptive Gauss-Hermite points)
• ICC?
• other

Not a high priority, just something that will save me a couple of trivial steps