- Add subpackage qtxdg-tools (Debian name qtxdg-dev-tools)

- Update to 3.4.0:
* Adds an command line MimeType (mimetype) tool
* Adds a command line Open (open) Tool
* Adds a command line Default App (defapp) Tool
* Adds a MIME Applications Associations (XdgMimeApps) class
* XdgDesktopFile:
- Deprecates XdgDesktopFileCache and drop XdgDesktopFileCache use
- Add explanation comment
- Avoid freeze for DBusActivatable apps
* CMake:
- Remove string conversion flags
- Removes not used helper function
* test:
- Use qAsConst()
* Build and Implementation:
- Don't use automatic string conversion
- Prevent a c++11 range-loop possible detach
- Fixed icon cache with absolute paths
- Use more precise wording
- Use the QString multi-arg overload
- Use qEnvironmentVariableIntValue()
- Use qAsConst
- Drop QRegExp.
- Port even more towards C++ raw string literal
- Port towards return with a braced init list
- Port towards raw string literal use.
- Use bool literals
- Ports towards C++11 override specifiers