Add first test for GeneralDataStream
Do not seek beyond start of content and add isValid()

seekToPreviousByte() does not seek beyond start of stream content anymore
and GeneralDataStream class now has an isValid() method that checks the
record type.
Five more tests for GeneralDataStream
Change tests to use port 8023 instead of 23
Removed unused header from mainwindow.cpp
Removed make install from travis-ci script
Improve test time and correctness

Improve tests in TelnetClientTests that assert that *no* message
is sent back to the server.
Merge branch 'master' into wip/write-to-display

Conflicts:
	lib/generaldatastream.cpp
	src/mainwindow.cpp
	test/unit/generaldatastreamtest.cpp