Add text block tests.
Implement book text block based on ftw.contentpage text block.
Rename paragraphs to textblock in tests and docstrings.
Update block LaTeX to render BookTextBlock instead of Paragraph.
Change validation viewlet to validate new BookTextBlock instead of Paragraph.
Change target release to 3.0.0.
Add upgrade step for replacing Paragraph with BookTextBlock.
Fix BookTextBlock name in GS type xml.
Rename Add Book Text Block permission for consistency.
Merge pull request #51 from 4teamwork/jone-refactor-textblock

Replace Paragraph with BookTextBlock.