Added icons for the new OSC plugins.
The switch plugin was severely crusty and in dire need of modernisation. To acheive this with a minimum of redundancy, the LinkedSlotGroup class has been updated to support arbitrary mixtures of static and dynamic slots and the switch plugin was rewritten to use this feature.
Fixed bug in the slider plugin. The parent node was not stored by the plugin which needed it to be. Also updated the ExpandableTextField support class to make it optionally possible for client plugin to force an update without firing one of the events it attaches to, since this approach would result in unterminated recursion. Updated the slider, const float and label plugins to match the new implementation and additionally improved the slider to delete invalid lo / hi input like the const float provider does and the slider and const float to update the text field in case of inappripriate input.