Add a custom Blockly toolbox

Provide several Blocks by default that allow to do things in XWiki.
Review common actions that need to be done in scripting and offer blocks for them.
For example: Ability to write XWQL queries to return a list of pages and ability to execute actions on them: replace content, copy, rename, delete. Send email. Etc. and other common scripting actions given here (https://www.xwiki.org/xwiki/bin/view/Documentation/DevGuide/Scripting/APIGuide/)