Better validation of TreeBASE id in study creation

This allows TreeBASE study ids in any of these formats, where '123' is a
study's serial identifier: 123, s123, S123, TB:S123, TB1:S123, TB2:S123.
Addresses #484.
Merge pull request #517 from OpenTreeOfLife/treebase-id-validation

Better validation of TreeBASE id in study creation