Add scripting docs and constness for check
Summary:
from calligra 2.9 090fdccbe35a3a46c32
addition of user oriented documentation for scirpting in reports.
Also added constness to scripting api functions
Test Plan: run 'doxygen' and check output
Reviewers: staniek
Reviewed By: staniek
Subscribers: KEXI
Projects: KReport
Differential Revision: https://phabricator.kde.org/D1335