feat(core): handle response content types

[JozefFlakus]

PR Type

What kind of change does this PR introduce?

[x] Bugfix
[x] Feature
[ ] Code style update (formatting, local variables)
[x] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[x] Tests

What is the current behavior?

• When trying to serve static files, responseHandler tries to JSON.stringify() every outgoing response.
• responseHandler doesn't detect mime-types automatically

Issue Number: #33

What is the new behavior?

• stream based fileReader
• integration tests for serving static files
• auto set response content-type based on provided body
• moved marbles.spec-util to common util folder
• added mock-fs, mime and file-type packages

Does this PR introduce a breaking change?

[ ] Yes
[x] No

[codecov]

Codecov Report

Merging #37 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master    #37   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          21     24    +3     
  Lines         230    283   +53     
  Branches       24     31    +7     
=====================================
+ Hits          230    283   +53

Impacted Files	Coverage Δ
...kages/core/src/response/responseHeaders.factory.ts	100% <100%> (ø)	⬆️
packages/core/src/response/responseBody.factory.ts	100% <100%> (ø)
...s/core/src/response/responseContentType.factory.ts	100% <100%> (ø)
packages/core/src/util/contentType.util.ts	100% <100%> (ø)	⬆️
packages/core/src/http.listener.ts	100% <100%> (ø)	⬆️
packages/util/fileReader.helper.ts	100% <100%> (ø)
packages/core/src/response/response.handler.ts	100% <100%> (ø)	⬆️

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[pdomaleczny]

What do you think of putting this path in some const and maybe you could use path.resolve here :D ?