L-function pages should display check functional equation info

[jvoight]

For me, that's highly convincing that the data is to be believed on the page (to what precision). Going forward, it would be nice if we included this as part of the out for precomputed L-series.

[davidfarmer]

This only makes sense for L-functions which are not computed rigorously.
Those will include higher degree nonarithmetic L-functions, such as from #6236 .