Support case-insensitive file systems in all sensors

Windows OS is case preserving but case-insensitive. Use the solution from CxxCompilerSensor for all other sensors.

Hints:
* I'm only able to test this on Windows. Maybe someone else can test it on Linux?
* Reconstruct case-sensitive path is time consuming. Not sure if this patch is a performance problem?

Changes:
* see #134
* call getCaseSensitiveFileName for all from CxxReportSensor derived classes (inside of saveViolation)
* add getCaseSensitiveFileName to CxxCoverageSensor
* add isSystemCaseSensitive to CxxUtils
* add test cases for isSystemCaseSensitive and getCaseSensitiveFileName