Delete Buttons on Coach Website

Some of the buttons on the coach website are hard to understand and not necessary for the coach to click:

• @scherlit checkbox in "theme controls" regarding "common knowledge" can be replaced by an additional config-information.
• theme-specific buttons should just be visible for the theme or not at all, because they are substituted by the structure-tree nodes.
• the "evoke" option in the angular-website is missing, which is why coaches can't command vSuS to raise arm before talking or repeat their answer. Therefore this needs to be fixed and the old teach-R coach website is recommended.

@scherlit please reassign this issue to me, once you are done with adding the config-option in the config file.