Fix and alter tinyMCE editor

Added <code> button that toggles the selection style
Removed buttons, added some other
Fixed problem with drop down menus, therefore kept the "Formats" menu for now.
Threw out some plugins, added some other.
Reworked capabilities of task builder

Changed text input fields to text areas.
Made them wider. Only vertically resizable.
Possibility to add source segments right away.
Introduced columns around the inputs in each row, to better manage them (dynamically adding new text areas for more solutions, etc.)
Backward compatible to formerly created tasks that might have solutions stored without an array.
Multiple solutions can be entered.
Merge branch 'ck_json_plus_taskbuilder' of https://github.com/cknoll/codequiz-server into ck_json_plus_taskbuilder
Revert merged commit.