cmake package autogeneration enabled & little findQwt.cmake fix

[p5-vbnekit]

This feature is made according to the following instructions: https://cmake.org/cmake/help/git-stage/guide/importing-exporting/index.html

Installed srsgui library can be easily imported from another cmake-project (modern way):

cmake_minimum_required(VERSION 3.15)
project("test")

find_package("srsgui" REQUIRED)

add_executable("test" test.cxx)

target_link_libraries("test" PRIVATE "srsgui::srsgui")

note: There's 2 commits... Obviously first commit is optional, but recommended. =)

[CLAassistant]

All committers have signed the CLA.