Instead of add_list and add_sqltable, the completion model now supports
add_category, and callees either pass in a SqlCategory or ListCategory. This
makes unit testing much easier.
This also folds CompletionFilterModel into the ListCategory class.
Now all completion models are of a single type called CompletionModel.
This model combines one or more categories. A category can either be a
ListCategory or a SqlCategory.
This simplifies the API, and will allow the use of models that combine simple
list-based and sql sources. This is important for two reasons:
- Adding searchengines to url completion
- Using an on-disk sqlite database for history, while keeping bookmarks and
quickmars as text files.
