Make Qt5/Qt6 versions fully coinstallable

Add version to the include path to make Qt5 and Qt6 versions coinstallable

Update WebServer example for 9ab612f

1.4.4 release

issue#173

Merge pull request QtExcel#157 from QtExcel/qt61

update qxlsx.pri for dll(so) project

Merge pull request QtExcel#148 from QtExcel/qt6beta

Qt6beta

Merge pull request QtExcel#145 from QtExcel/qt6beta

Qt6beta

Merge pull request QtExcel#141 from QtExcel/qt6beta

- testing in Qt 6.0.1

Merge pull request QtExcel#126 from QtExcel/qt6beta

Qt6beta

Merge pull request QtExcel#114 from DarthGandalf/install

Install the library, findable by find_package()