Keeps causing linker to fail

* travis-ci add more caching

* travis-ci move doxygen to semaphoreci

* travis-ci move linux debug to semaphoreci

* travis-ci try ccache on OSX and android

* travis-ci ccache stats

* try again

* Attempt to prepend ccache to qmake command

* Test enabling ccache for ios too

* Deploy ccache from S3 per @dagar

* Revert "Test enabling ccache for ios too"

It was a nice thought.

This reverts commit 7e7aeb367696ee9c8abc5cc8122dcd35196d96bb.

* Try to optimally set the number of make jobs

* Fix job estimation and disable ccache on android

* Android: reenable ccache and disable parallel jobs

* Check if android build passes with 4 workers

* Try to parallelize xcodebuild too

* Give mac builders an extra worker and pretty up the ios build output

* Add make output filtering with correct exit code, no sudo or ccache on ios build

* Try wrapping ccache to enable use on xcodebuild

* Make ios ccache helpers executable

* Turn back on pretty printing for IOS

* Show some ccache stats on IOS build to see if we're getting hits

* Change android build OS type to linux

* Require trusty for android build

* Require sudo for android so we get trusty

* Maybe this will function properly on edge?

* Try to use stripped binary bzips

* Screw it! Run android on precise again

* Back to the original android build configuration. I give up

* Qt5.5.1 link corrected.

* Qt5.5.1 tarball saves to project's root directory
since qt_deps_tarball used to have prefix of /vagrant.

* Add requests to update machine setup for both Travis and Vagrant

* Vagrant: use config variable in place of static string

* Vagrant: init and update submodules

* travis-ci install gstreamer

* update linux gstreamer dependencies

* fixes #2540

* travis-ci doxygen to trusty

-closes #3479