SCIM Qt5 Input Method Plugin

This code is adopted from SCIM Qt4 counterpart, using the qmake build
system.  Integration of qmake to autotools is possible in the future.

To build and install,

1. build scim, including the im-agent.
2. change to this directory and call `qmake`
3. make
4. make install

Reference:
1. Debian packages gcin-qt5-immodule, uim-qt5-immodule
   libfcitx-qt5-1 (dbus), ibus (dbus)
2. https://www.kdab.com/qt-input-method-depth/