Remove alpha prefix from tree tag

[ashenkin]

Right now, the forestplot importer adds a "T" to all trees imported, and all the other importers expect that code to be there, and will also add an "I" when appropriate. Really, the tree tag should not have that "T" or "I" prefix. So, this should be fixed in the forestplots importer, and all the other importers, queries, etc. The earlier we do this, the easier.