Docs

- added a onSelect event for lists
- added docs for onSelect
- added addPlugin and addObject docs

docs/objects/List/onSelect.md

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+## onSelect
+
+### Description
+
+`onSelect(self, event, item)`
+
+The onSelect event is triggered when a item on the list gets selected.
+
+### Returns
+
+1. `object` The object in use
+
+### Usage
+
+* Add an onSelect event to a list:
+
+```lua
+local basalt = require("basalt")
+
+local main = basalt.createFrame()
+local list = main:addList()
+
+list:addItem("Entry 1")
+list:addItem("Entry 2")
+
+function listOnSelect(self, event, item)
+  basalt.debug("Item got selected:", item.text)
+end
+
+list:onSelect(listOnSelect)
+
+basalt.autoUpdate()
+```