Adding ODT example to storybook and fixing variorum bugs

[ajolipa]

In this PR

• Fixes bug in variorum mode where folios in different documents with the same folioID were not being stored properly in the component state: when in variorum mode, folios are now stored internally with the ID [documentID]_[folioID] to avoid collisions;
• Updates the viewportState function to track the associated document of the currently selected folio, so that if you navigate back to the grid view from a folio in variorum mode, the document that folio came from will be automatically selected;
• Updates Storybook to use the ODT project as the example for the variorum feature

[ajolipa]

Update: Now also addresses Issue #118 by removing the blue highlighting from the "current folio" in grid mode.

[ajolipa]

Further update: Now includes a fix to the resizing functionality of the split pane view so that it now works with touchscreen devices as well as mouse clicks.

[ajolipa]

Further update: Now also includes a trigger to reload the document data in the case that the component props change without the user navigating to a new page. (See PR #123 )