[FIX] ProjectPreprocessor: Fix dependency processing

[Thodd]

Resolves #166

NPM dependencies which cannot be configured (via yaml or shim) are
considered invalid and should not be part of the final project tree.

[CLAassistant]

All committers have signed the CLA.

[coveralls]

Coverage increased (+1.0%) to 83.31% when pulling f93989c on fix-preprocessor-dep-handling into 56b55f2 on master.

[coveralls]

Coverage increased (+1.0%) to 83.31% when pulling c25ae03 on fix-preprocessor-dep-handling into e3f804d on master.

[RandomByte]

The dependencies issue label is meant for npm dependency updates/changes to this project. Such as the dependabot pull requests.

[RandomByte]

Nicenstein 🎉

[RandomByte]

Minor remark: You may rename the commit message to

[FIX] ProjectPreprocessor: Fixes dependency processing

Also see https://github.com/SAP/ui5-tooling/blob/master/docs/Guidelines.md#commit-summary:

It shall be written in imperative present tense (as recommended by Git)
Examples: Instead of "Adding tests for" or "I added tests for" use "Add tests for" or "Add feature xy".