update visual summary panel when user moves through corpus list without mouse-clicking

[kvesik]

Current behaviour:

• when user clicks on an entry in the corpus list, that row is highlighted/selected, and the visual summary panel is updated with that sign's modules
• when user moves up and down through corpus list with arrow keys or by pressing an alphabet key, the next row is highlighted, but the visual summary is still set to the entry that was last clicked

Desired behaviour:

• using keyboard keys should update visual summary to reflect which sign is highlighted in the corpus list, just like mouse-clicking does

[kvesik]

rolled into #105