Merge pull request #1 from n-educatio-pl/master

Added filter functionality.
Merge pull request #2 from n-educatio-pl/master

Added Shell view used when rendering Response
Merge pull request #3 from n-educatio-pl/master

Multiline response rendering.
moved shell commands to more meaningful Command namespace
All command related classes moved to Command namespace
Executor class refactored and made stateless
Introducing Validator that ulimatelly will be responsible for verifying files against various tools,e.g. static code analysis