Removed action checkboxes and respective buttons and JS 'links'

Can someone please check this thoroughly? I am not too
familiar with the code and might have missed or
misunderstood something.
Also, there is one thing left to do: Instead of the
row of action buttons should be one single 'Disable
all plugins' button. That still needs to be implemented.
Meanwhile no button gets displayed at all below each
list of plugins.