support treebank metadata

[balmas]

When alpheios is enabled in the alignment editor, we want to support the ability to bring up the tree displays for the texts that are being aligned.

The tokenizer service input parameter tbsegstart can be used to specify the starting sentence metadata for aligned words, but we also need to allow the user supply the url of the treebank in the metadata for the text.

assigning to myself to work through the requirements more fully.