Create default .gitignore files within new project

[Dominik Braun]

A new project can be created using verless create project <name>. This freshly created, fully initialized standard project should contain a .gitignore file by default:

# File: .gitignore
generated/

The contents of this file can be stored in core/defaults.go and created along with the other files in core.CreateProject.

[Samyak Bakliwal]

What should we include in .gitignore file ? or create just an empty file ?

[Dominik Braun]

There should be at least one entry: generated/. The reason is simple:

#160 introduces pre-build commands you can use for generating any files you want, and #166 will introduce pre-build commands for themes you can use to generate CSS or JS. Those generated files should be stored inside a directory called generated - we support a generated directory in the project root and a generated directory in each theme's directory.

[Dominik Braun]

Fixed with #179.