Delete rows

[saschaishikawa]

Enables users to delete entire rows at a time, instead of having to delete each annotation individually. Resolves issues #92, #124.

Note: As before, each annotation can be deleted separately by clicking on it. However, when deleting an annotation that belongs to a row, I was forced to add a UI to clarify what the user wants to do: delete a single annotation or an entire row? (see below)

You click on individual annotations to delete them, or the rows containing them. There's no other way to distinguish. One solution would be to introduce a "delete" button on each annotation and an additional button at the end of each row.