Replace #[macro_use] with normal use

[luleyleo]

druid-shell/src/lib.rs#L27

#[cfg(target_os = "windows")]
#[macro_use]
extern crate winapi;

#[cfg(all(target_os = "macos", not(feature = "use_gtk")))]
#[macro_use]
extern crate objc;

#[cfg(not(any(feature = "use_gtk", target_os = "linux")))]
#[macro_use]
extern crate lazy_static;

#[cfg(all(target_os = "linux", feature = "x11"))]
#[macro_use]
extern crate lazy_static;

This is no longer necessary with Rust2018 and should be replaced with use statements in modules that actually utilize those macros

[totsteps]

@Finnerale would love to fix this.
I know the very basics of rust. But here's how I will approach this. Please correct me if I am wrong.

1. Remove all use of #[macro_use] from druid-shell/lib.rs file.
2. Import macros using use.
   For example, in platform/mac/application.rs file I need to add the following line
   use objc::{class, msg_send, sel, sel_impl};.

Thanks.