Progress bar for loading files

[AlistairNWard]

Loaded the bookmarks for RareVariantVis and it takes a while (there are 390 bookmarks). I wonder if it would be worth putting in a progress bar for this, and maybe when loading variants too. It's practically instantaneous to get the number of lines in the file, so we could easily include a progress bar while bookmarks are loading. Seems like we could do the same easily for variants when we select a new gene.

Thoughts?

[tonydisera]

It like your idea. I think if the transcript is included, the bookmarks would load in under a second. Right now, gene has to get the canonical transcript for each bookmarked gene.