First implementation of GasStation interface.

Need to test it and optimize todos
disable inspection SynchronizationOnLocalVariableOrMethodParameter
Add junit dependency to pom.xml and configure repositories
Update tests

Rename threads and simplify code
reimplement multithreaded test that is safe from mantissa presicion point of view
buyGas: return cost instead of revernue
removed todo about synchronized proxy

There is no sense to create syched proxy for gas pumps because they come from outside and
any can keep the reference to the original pump and do whatever without synchonization and
our efforts will be useless.
Simple test for default values
Add logging to configuration
Implement multithreaded test with revenue
Log4j will show only errors
Show warnings instead of errors, add exceptions tests
Add own log4j config to tests to see debug level
Revise TODO

stick to unmodifiable implementation
Review TODO non-blocking

Additional implementation will take additional synchronization for
caching, ordering and locking
Merge branch 'feature/gas-station-impl' into develop

Implementaion of GasStation that can provide service in multithread mode