Fixed too broad condition to identify last page in 1997 docs.
Simplified code to merge LTNetworks.
Moved column identification from LAOrganizer to LawConverter.
Fixed wrong test case and respective code.
Major improvement to interpretation of PDF.

- Added centered_column, that gets all centered text.
- Removed need of offset to compute column-centered titles.
- Fixed failing test in order of appearance of table and column.
- Tables and Images are now added directly to columns.
Fixed error on aligning points due to list change during iteration.
Removed unused import.
Removed unneeded parameters from ConverterParameters.
Added list of all tables to LawConverter, exposed via .tables.
Implemented fixed width columns. Improved most parser test cases.

The converter now sets the column.x0 and x1 depending on the year
of the document, instead of computing it on the fly. The problem
was that some pages had fully cited text, leading to a shift of
the x0 and x1 and thus generating variable results that depended
on the content of the particular column.

Also, most test cases of a full document now assert the number of
titles of the full document.

Also, the identification of subparagraph and subline was moved to
ConverterParameters, fixing a todo.
Renamed html.Line to html.Paragraph and added paragraphs property.
TestParser now asserts for number of titles. Improved parameters.