Package search

In a plugin tool window (see #4) there should be a reactive package search functionality, like the NuGet one:


(we may add various Conan-related settings to the panel, such as source selector, but that's not necessary; basic search is okay)

Search should start automatically when the users enters any text. It should cancel the previous attempt if the user changes the text entered, and it shouldn't try to spawn too much processes (I suppose that's more or less the standard reactive search box functionality).