CI & Toolchain

Improves CI pipeline and adds gitlab templates.

New Features

• [CI]: Runs unit tests in debug and relwithdebinfo build type
• [Gitlab-Templates]: Added templates for merge requests and issues
• New feature table in Readme

Refactoring

• [io]:
  • Network Socket tests are now an example application --- Corresponding unit tests depended on timing.
• [parallel]:
  • Removed fixed timeouts from unit tests.
  • Removed console output from unit tests - if you get the impression console output is necessary to test this use Google Mock!