Make it super simple to use on Travis CI

A common use case for linuxdeployqt is to use it on Travis CI after the make command.

Currently quite some hoops are necessary. We should make linuxdeployqt so intelligent as to be a one-line operation, ideally replacing most of the manual work of

language: cpp
compiler: gcc
sudo: require
dist: trusty

before_install:
    - sudo add-apt-repository ppa:beineri/opt-qt58-trusty -y
    - sudo apt-get update -qq

install: 
    - sudo apt-get -y install qt58base
    - source /opt/qt58/bin/qt58-env.sh

script:
  - qmake PREFIX=/usr
  - make -j4
  - sudo apt-get -y install checkinstall
  - sudo checkinstall --pkgname=app --pkgversion="1" --pkgrelease="1" --backup=no --fstrans=no --default --deldoc 
  - mkdir appdir ; cd appdir
  - dpkg -x ../app_1-1_amd64.deb . ; find .
  - cp ./usr/share/applications/*.desktop .
  - cp ./usr/share/icons/hicolor/48x48/apps/*.png .
  - cd .. 
  - wget -c "https://github.com/probonopd/linuxdeployqt/releases/download/3/linuxdeployqt-3-x86_64.AppImage" 
  - chmod a+x linuxdeployqt*.AppImage
  - unset QTDIR; unset QT_PLUGIN_PATH ; unset LD_LIBRARY_PATH
  - ./linuxdeployqt*.AppImage ./appdir/usr/bin/* -bundle-non-qt-libs -qmldir=$(readlink -f /opt/qt5*/qml/)
  - ./linuxdeployqt*.AppImage ./appdir/usr/bin/* -appimage -qmldir=$(readlink -f /opt/qt5*/qml/)
  - find ./appdir -executable -type f -exec ldd {} \; | grep " => /usr" | cut -d " " -f 2-3 | sort | uniq
  - curl --upload-file ./APPNAME*.AppImage https://transfer.sh/APPNAME-git.$(git rev-parse --short HEAD)-x86_64.AppImage

We could, as part of linuxdeployqt and/or the underlying appimagetool,

[ ] Unset the offending Qt environment variables that prevent linuxdeployqt from running
[x] Remove the need for -qmldir=$(readlink -f /opt/qt5*/qml/)
[ ] Check if there is exactly one desktop file in usr/share/applications and if so, use that. Otherwise have the user specify the desktop file rather than the executable and figure out the executable and icon from there, hence doing the copying automatically
[ ] Use checkinstall. This is because I could not figure out a reliable method of installing to a different location than /usr - seems not needed in most cases
[ ] Optionally, use the git and/or travis information to determine the version
[ ] Optionally, upload to transfer.sh

In the current continuous build, the following is implemented:

language: cpp
compiler: gcc
sudo: require
dist: trusty

before_install:
    - sudo add-apt-repository ppa:beineri/opt-qt58-trusty -y
    - sudo apt-get update -qq

install: 
    - sudo apt-get -y install qt58base
    - source /opt/qt58/bin/qt58-env.sh

script:
  - qmake PREFIX=/usr
  - make -j4
  - sudo make INSTALL_ROOT=appdir install ; sudo chown -R $USER appdir ; find appdir/

after_success:
  - wget -c "https://github.com/probonopd/linuxdeployqt/releases/download/continuous/linuxdeployqt-continuous-x86_64.AppImage" 
  - chmod a+x linuxdeployqt*.AppImage
  - unset QTDIR; unset QT_PLUGIN_PATH ; unset LD_LIBRARY_PATH
  - ./linuxdeployqt*.AppImage ./appdir/usr/share/applications/*.desktop -bundle-non-qt-libs
  - ./linuxdeployqt*.AppImage ./appdir/usr/share/applications/*.desktop -appimage
  - find ./appdir -executable -type f -exec ldd {} \; | grep " => /usr" | cut -d " " -f 2-3 | sort | uniq
  - curl --upload-file ./APPNAME*.AppImage https://transfer.sh/APPNAME-git.$(git rev-parse --short HEAD)-x86_64.AppImage

Note that if qmake does not allow for make install or does not install the desktop file and icon, then change it similar to https://github.com/probonopd/FeedTheMonkey/blob/master/FeedTheMonkey.pro.

probonopd / linuxdeployqt

Make it super simple to use on Travis CI #81