[update] update to upstream 5.1.0-beta1
Squashed 'qtimageformats/' changes from bacb0be..f293cc8

f293cc8 disable module when gui is not available
7e58610 Doc: Fix module name in .qdocconf
647a723 Fix MNG imageformat plugin build.
847c2eb Fix tiff imageformat plugin build for WEC7.
8cdee97 Merge branch 'release' into stable
a2cd7f7 Fix the config.tests to correctly detect the 3rd party libraries
5073146 Fix compilation for Android.
4b1c277 Bump MODULE_VERSION to 5.1.0
1b8090c Merge branch 'dev' into stable
3e7042f Merge remote-tracking branch 'origin/release' into stable
313d60c Fix glitch on MNG animation Loops when QMovie caching is enabled
e86c435 sync.profile: Point dependencies to 'refs/heads/dev'

git-subtree-dir: qtimageformats
git-subtree-split: f293cc8539da5d4ea915c957abbba473515793ad
Merge commit '8ac8f942de5c00f6cd15f0cc0fa99d68d97f1622'