TSLint: Support for excluding files and folders (simplified)

[vbolshutkin]

Short description of what this resolves:

Sometimes we might want to exclude files from linting, i.e. autogenerated files, stub files etc. TSLint does support this in its tslint.json file, but ionic-app-scripts overwrite that field with {typeCheck:false}

There's another pull-request #1204 for the same purpose, but it is a bit more verbose, a bit outdated and in case of appearing new linter options supported by TSLint we will apply the same fixes once again

Changes proposed in this pull request:

• Use Object.assign to add {typeCheck: false} to linterOptions and preserve original options

[vbolshutkin]

Perhaps, a duplicate of #1463