Modify Thetas Shiny Graphing file loading behavior

[ChaochihL]

Feature suggestion mentioned at the end of issue #47:

Because I'm working with a non-model organism with ~11,500 scaffolds (as opposed to something nice like 23 chromosomes...) when you upload the {name}_Thetas.graph.me to Shiny it's a super long list that's initially populated due to the unique call within the server.R script (line 109). Is there a way so that you can start by loading the file and insert the Scaffold of interest, rather than removing the 11,499 scaffolds you don't want, as a default? My current solution is to create a subsetted graph.me file with just the scaffold(s) I want, and that works fine, but thought it would be a feature to consider.