Make BEAUti template more like standard tempate

[rbouckaert]

The way priors are handled is a bit ad-hoc, and inflexible, e.g. no way to specify a birth-death prior if you wanted to in BEAUti, or log-normal prior on theta's.

[rbouckaert]

Also, the gamma distribution is parameterised different (shape, rate) than the Gamma distribution in BEAST (shape, scale), which is terribly confusing for users.