Adds Qt5TranslationLoader cmake module

It can automatically load translations on Qt5. It works with libs and apps.
Removes lxqt_translate_desktop() from the _use.cnake

It's already present in the modules.
Removes duplicates add_definitions()
Removes cmake commented code
Copied Qt5LinguistToolsMacros.cmake

Copied from:
https://qt.gitorious.org/qt/qttools/source/a1751e3d586f1ebfb1770392e52d7c1648a7406f:src/linguist/Qt5LinguistToolsMacros.cmake
Fixes Qt5LinguistToolsMacros file extension bug

get_filename_component and name_we are used get the base of the
translations filename. But, NAME_WE, takes everything after first dot as
the file extension. Which means that two files:
	lxqt-config-session_zh_CN.ts
	lxqt-config-session_zh_CN.GB2312.ts
will have the same basename(lxqt-config-session_zh_CN) which is just plain
wrong, for our purposes. This wrong computation leads to an target names
collision that least to cmake configure errors.

Just replaced get_filename_component and NAME_WE to get a proper basename.
Use the new LXQtTranslate modules.

Eating our own dog food.