* notifications: free cairo images on destruction
asan reports a leak on exit if we dont free the image we created in the
draw function. add a destructor and free images on exit.
* compositor: destroy wlroots types on exit
there are a few types not being destroyed on exit and causing a leak on
exit in wlroots reported by asan, add those.
* cursormgr: ensure we destroy cursor mgr on exit
add a destructor and call wlr_xcursor_manager_destroy on the manager on
destruction, leak reported by asan.
* keybindmgr: free state and keymap
add missing keymap_unref on creation, and add a destructor and free the
state on exit. leak reported by asan.
* skeyboard: add destructor and free state
free the state on destruction of keyboard, reported as leak by asan
