gradebook 6.x-2.0-beta1

Changes since gradebook-6.x.1.0-RC1:

• #360414 by MGN: Added new feature to delete gradebook grades when account is deleted.
• #360407 by MGN: added export gradebook feature, borrowing heavily from the webform module. This adds a menu local item to export the gradebook to Excel or text file. Most of the new code is in two include file gradebook_report.inc and gradebook_export.inc. To avoid code duplication, gradebook_gradebook_page() was modified to return rows for a text table when called with the argument = TRUE.
• by MGN: rewrote hook_gradebookapi_teachers and hook_gradebookapi_students so creating a new drupal role does not automatically give it teacher and student status. Also separated out common code into a helper function _gradebook_gradebookapi_role to avoid code duplication.
• #358236by MGN: incorrect use of url() in form redirect.
• by MGN: updating README.txt
• by MGN: Added two forms and modified gradebook_page to improve UI.
• Added form to grade all students for a select assignment, another to grade all assignments for a selected student.
• Added divs for form elements to permit form layout through CSS (not yet implemented in gradebook.css).
• Split off page callbacks into either gradebook.pages.inc (display/edit grade) or gradebook.category.inc to reduce size of gradebook.module.
• Reworked theme_gradebook_page and gradebook.css to improve css control of formating on gradebook_page.
• Added assignment class average row to gradebook_page.
• by MGN: fixed bug in update from 6.x.1.x to 6.x.2.x
• by MGN: adding install file for gradebook.module
• by MGN: add date support to gradebook 6.x.2.x development