I don't recommend ignoring .abproject file as it is a vital part of the project structure since the last release. Using it we unified all projects created via our clients so they can opened in any of them.
As for the way to ignore files, there is no option yet to do that in a project created by AppBuilder using our version control feature because you don't have an access to .gitignore file in the cloud. However you can push your project to a third party repository
like GitHub. Then you will have access to .gitignore file and edit it.
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