Fix a typo in variable name

Signed-off-by: Luís Pereira <luis.artur.pereira@gmail.com>
Cleans commented unneeded stuff

Signed-off-by: Luís Pereira <luis.artur.pereira@gmail.com>
Fixes extra misleading slashes in path names

There was pathnames with two slashes in a row.

Signed-off-by: Luís Pereira <luis.artur.pereira@gmail.com>
Removes duplicate installation of a file

Signed-off-by: Luís Pereira <luis.artur.pereira@gmail.com>
Removes another duplicated installation of a file

Signed-off-by: Luís Pereira <luis.artur.pereira@gmail.com>
Find liblxqt dependencies automatically

When the user writes something like this:
        find_package(LXQT5 REQUIRED)
        include(${LXQT_USE_FILE})

It shouldn't need to to find LXQT dependencies.
That's what was happening when the build type was set to debug.

Signed-off-by: Luís Pereira <luis.artur.pereira@gmail.com>
Don't use undefined variables

When using Qt5, QT_QTCORE_LIBRARY, QT_QTGUI_LIBRARY, QT_QTDBUS_LIBRARY
QT_QTCORE_INCLUDE_DIR, QT_QTGUI_INCLUDE_DIR and QT_QTDBUS_INCLUDE_DIR
are undefined.
We should not use them.

Signed-off-by: Luís Pereira <luis.artur.pereira@gmail.com>
Use the same header namespace everywhere

We must use the same header namespace in in-tree builds and in install
builds. Otherwise the user will get an FTBFS when moving from an install
build to an in-tree build or vice-versa.

Signed-off-by: Luís Pereira <luis.artur.pereira@gmail.com>
Updates the Qt4 and Qt5 library names and related stuff

Qt4 library name is liblxqt. The prefix for install path is lxqt. It
remains untouched.
The Qt5 library name is liblxqt-qt5. The prefix for install path is also
lxqt-qt5.

Signed-off-by: Luís Pereira <luis.artur.pereira@gmail.com>
Don't allow #include <lxqt-qt5/lxqtxxxxx.h>

#include <LXQt/Xxxxx> is the way to go for both Qt4 and Qt5.
#include <lxqt/lxqtxxxxx.h> is allowed, with Qt4, for compatibility reasons.

New code should use #include <LXQt/Xxxxx>

Signed-off-by: Luís Pereira <luis.artur.pereira@gmail.com>