Include some Clang-Tidy checks

[bassoy]

The configuration file excludes clang-tidy checks

google-readability-braces-around-statements
google-explicit-constructor
hicpp-vararg
cppcoreguidelines-pro-type-vararg

We should include them.

• google-readability-braces-around-statements requires simple refactoring
• google-explicit-constructor needs significant rework also in the test files and results in API change
• hicpp-vararg needs usage of the boost lightweight unit test instead of the boost-test