Plugin settings

Add plugin settings concept and a plugin settings window in the IDE Settings window.

There should be one setting to configure: name of the Conan executable file.

Although I'm not sure if Conan executable will work without defining a correct Python virtualenv, so we'll need to conduct some testing and determine if we need to add a virtualenv selector.

The issue names no files, tests, or entry points. Start by surveying the plugin's existing IDE settings integration and testing how the Conan executable and any Python virtualenv are discovered; done means a settings window exposes a working executable setting and the need for a virtualenv selector is resolved.

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