Review changes made for Issue #53 CMake

I've made all the CMakeList files the project needs. I managed to get the project to build, compile and install. However, when I try to run the qmlscene ui/main.qml, it can't seem to find the directories where the plugins are installed. Could you have a look?
I had credited CMake with doing all of this, but you were the one who figured it out.  Sorry for the slight!

But I think there's a shorter way to do it:
```
set_target_properties(epubreaderplugin PROPERTIES
    LIBRARY_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/../${PLUGIN_DIR}
)

# Copy the qmldir file to the build dir
add_custom_command(TARGET epubreaderplugin POST_BUILD
    COMMAND ${CMAKE_COMMAND} -E copy ${CMAKE_CURRENT_SOURCE_DIR}/qmldir ${CMAKE_CURRENT_BINARY_DIR}/../${PLUGIN_DIR}
)
```
The first command sends the `.so` file to the correct directory.  We still need to copy over the `qmldir`, and we need to do that whether we're doing an in-tree or out-of-tree build.