Update BEAUti fxtemplates to BEAST3 spec classes

[walterxie]

See #139

Updates the BEAUti template XMLs (ClockModels.xml, ParametricDistributions.xml, Standard.xml, SubstModels.xml, TreePriors.xml) to point at the new beast.base.spec.* implementations instead of the legacy beast.base.* classes, especially <map, and bumps the <beast version='...'> attribute from 2.0 to 2.8 in all five files.

Key changes:

• Distributions: Dirichlet, Poisson, and the full set of univariate/multivariate/conditional distribution entries in Standard.xml (Bernoulli, Beta, Cauchy, ChiSquare, Exponential, Gamma, LogNormal, Uniform, IID, OffsetInt/Real, TruncatedInt/Real, etc.) now reference beast.base.spec.inference.distribution.*. OneOnX was removed (noted in comment).
• Parameters: parameter.RealParameter usages replaced with the new spec parameter types (RealVectorParam, RealScalarParam), including domain='PositiveReal' attributes where applicable (e.g. popSize, Poisson.lambda).
• Substitution/tree/clock models: JukesCantor, RandomTree, ConstantPopulation and related inputLabelMap/inlinePlugins/stateWithoutInitialization entries updated to beast.base.spec.* equivalents; duplicate/legacy (non-spec) entries removed from Standard.xml's config lists.
• Standard.xml formatting: block re-indented and reorganized with comments grouping univariate/multivariate/conditional distributions.

Additional:

• CloneTest.java: added a tracking comment (Relaxed clock subtemplates not yet ported to BEAST 3 ClockModels.xml #136) above the @disabled relaxed-clock subtemplate test, documenting why it's still skipped.

[walterxie]

Random local clock using new template:

rc.xml

[jordandouglas]

InverseGamma should also be included in the map. But otherwise looks good to me

[walterxie]