Add copyright info to build process, bump copyright year in LICENSE

[sedge]

It would be nice to have the build process prepend copyright info to our distribution file.

[humphd]

I can't figure out if this is still necessary, given that we have it in a) github; b) npm;

I can't see an obvious way to accomplish this with parcel. So we'd need to write a script to just prepend it to the built files. Probably the cleanest way to do this is via an SPDX comment:

/** 
 * Copyright 2013 - 2018, Alan Kligma and the Filer contributors
 * SPDX-License-Identifier: BSD-2-Clause
 */

Also, we should update LICENSE to include 2019 soon.