Add copyright and license to source as comments

[llucax]

There are a few things to review about the license:

• The LICENSE file includes a section on how to apply the license, this should be removed. (this is part of the license and the license can't be changed)
• The license should be applied as it is said in the LICENSE (add copyright notice to source files, etc.).
• Add the license text to the app itself (about box/terms of service/etc.). Moved to Add the license text to the app itself (about box) #24.