Paginate library getter

[arrudagates]

Right now, the get_library function waits until it has the whole library to display it to the user, freezing the rendering in the process. This is fine for small libraries, but testing with my almost 700 tracks library makes it freeze for 10 to 15 seconds before anything happens after the library command runs.
The solution to this is paginating the command, so we fetch a fixed number of tracks from the library and fetch more when the user starts approaching the end of the current page's list/