add BuildOptions class in tools/config.py + unit tests for it
flesh out DictObject, extend list of required configuration variables, initialize global VARIABLES through config.init() function
fix unit tests w.r.t. changes in tools.config module
use ConstantDict from vsc.utils.missing
get rid of nonsense test
enhance Enhanced testcase
Merge pull request #884 from boegel/enhance_enhancedtestcase

enhance Enhanced testcase
Merge branch 'develop' into cleanup_build_options
update vsc-base
use FrozenDictKnownKeys rather than ConstantDict, adjust unit tests accordingly
fix module_generator unit tests, reinitialize config where needed
fix easyconfig unit tests, implement standard setUp and tearDown in EnhancedTestCase
minor import cleanup
add super calls for setUp/tearDown in asyncprocess, config unit tests; extend setUp/tearDown in EnhancedTestCase
clean up and fix easyblock unit tests
add super calls for setUp/tearDown in filetools & github unit tests
add super calls for in remaining unit test modules, clean up imports
clean up ConfigurationVariables class, move mapping of oldstyle to newstyle keys to a dedicated function
add missing frozendict module
make ConfigurationVariables and BuildOptions singletons, adjust unit tests accordingly