Enable support for Qt5

Since Qt4 is EOL, we should also support libcommuni build with Qt5.
In order not to break Fedora docker builds, -DENABLE_QT4 is introduced.

When set to 'ON', support for Qt4 is being enabled,
otherwise support for Qt5 is enabled.

Signed-off-by: Conrad Kostecki <conrad@kostecki.com>

cmake: cleanup configuration

* rename CMake modules to follow CMAKE_MODULE_PATH matching rules
* fix git ignore rules to not ignore CMake modules
* add CMake module to find jsoncpp without pkg-config
* drop unused/outdated modules

Switch from boost shared pointers to stl shared pointers (#162)

* Swiften 4 support
* using standard shared pointers when compiling with Swiften 4