atom-editor: Bump version, cleanup depends and build process

* Bump version to 0.155.0

* Remove the following dependencies:
 * libatomic_ops: Indirectly already satisfied by base-devel
 * libgcrypt: Already satisfied by libgnome-keyring

* Build inside of current directory instead of /tmp

* Properly separate prepare(), build() and package()

* Unify atom-python.patch of atom-editor and atom-editor-git