Adds portable headers

The non portable headers can still be used. The portable headers work fine
with Qt4 and Qt5 as usual. New code should use them.
The header namespaces are LXQtGlobalKeys and LXQtGlobalKeysUi.
The LXQtGlobalKeys portable headers are: Client, Action and
LXQtGlobalKeys.
The LXQtGlobalKeysUi portable header is: ShortcutSelector.

Signed-off-by: Luís Pereira <luis.artur.pereira@gmail.com>
Adds include_directories() to the _use.cmake file

Signed-off-by: Luís Pereira <luis.artur.pereira@gmail.com>
Updates translations files install destination

Qt4 and Qt5 versions must be installed on different locations.

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