[typescript-angular] Angular 7 compatibility of dependencies and package generator

Created by: pkainz

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\.
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@TiFu (2017/07) @taxpon (2017/07) @sebastianhaas (2017/07) @kenisteward (2017/07) @Vrolijkx (2017/09) @macjohnny (2018/01) @nicokoenig (2018/09) @topce (2018/10)

Description of the PR

Fixes: https://github.com/OpenAPITools/openapi-generator/issues/1612

Parameterized mustache file for compatible dependencies for different Angular (also v7) versions (with known major changes). Variable changes comprise:

• useRxJS6: removed from package.mustache, only used in api.service.mustache and apiInterface.mustache to control the correct imports of Observables
• ngPackagrVersion : added (not accessible via CLI's --additional-properties)
• useOldNgPackagr : changed usage: false adds the tsickle dependency and its tsickleVersion)
• tsickleVersion: added (not accessible via CLI's --additional-properties)
• rxjsVersion: added (not accessible via CLI's --additional-properties)
• zonejsVersion: added (not accessible via CLI's --additional-properties)
• tsVersion: added (not accessible via CLI's --additional-properties)