Add generating context blocks; add entry limit and context size to GUI

- Add calls to Begin/EndContextBlock in SummaryGenerator
- Add controls to toggle generating context in report, set context size and
  limit number of file entries in generated report
- Fix tests so hat they use new IDocumentBuilder interface
Add DocumentBuilderFactory + tests
Make SearchSummary use DocumentBuilderFactory

- Make the module actually use DocumentBuilderFactory
- Make DocumentBuilderFactory.Create case-proof
- Add DocumentBuilderFactory test case for valid format, invalid case
- Remove 'File name' checkbox from GUI (force it being written every time)