The patch provides mechanism for setting custom plugin name for `DetectedProblem` instances. Old version always return generic `i18n("Plugin")` value form `sourceString()`, which leads to necessity to create problem sublasses which only overloads single `sourceString()` methodadds new class `KDevelop::PluginProblem` which allows to avoid create subclasses of `KDevelop::DetectedProblem` with only overloaded `source()` and `sourceString()` methods for every plugin (cppcheck/valgrind for example).