Android: Release the surface texture when not in use

With some Android versions the preview texture is released when the
application is suspended. If we don't release the texture in our
code, the preview will be empty when the application resumes.

Task-number: QTBUG-38165

Change-Id: I72244727081d8f94ee5f6cb0ab660ca59f4bb2de
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>
Doc: Improved example documentation

-added instructions on how to run the example
 (using \include to insert a section from qtbase/doc/global/)
-updated copyright year
-removed links to Qt 4 API
-rearranged some of the sections
-created links from the example pages to Qt Multimedia
-fixed QDoc warnings related to the example pages

Task-number: QTBUG-33597
Change-Id: Id45ce5cbd40dbfa384abd7260a316f6f6837c186
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>
Reviewed-by: Sze Howe Koh <szehowe.koh@gmail.com>
Rework qmlvideofx example

Task-number: QTBUG-38121
Change-Id: If06ba6ce2c66b4d735baaeb56e004861c62ea533
Reviewed-by: Alessandro Portale <alessandro.portale@digia.com>
Merge remote-tracking branch 'origin/release' into stable

Change-Id: Ieb521fb1e9f297a167eea19c771cb5915c01df97