Support for Go modules

[Baldomo]

It's now been several months since the official go mod tool was released. It is (so far) impossible, however, to use this package inside of a moduled project without resorting to GOPATH hacks or installing packages in GOPATH, then disabling the modules system and running qtdeploy. A solution to he whole ordeal could be generating qt inside the $GOPATH/pkg/mod and providing/generating a go.mod file. This way, a replace directive can be used to load the module from local storage.

PS I'm on Windows and Go 1.11

[therecipe]

Hey

I will look into this.

[therecipe]

Okay, it should be possible now to use this inside a moduled project with 8610850
however some things like the -fast and -qt_api flags and the docker support won't work yet.

It currently works by using go mod vendor and go build -mod=vendor under the hood.
I looked into the "replace" directive as well, but since there might be the need to also generate code with "qtrcc" and "qtmoc" for 3rd party packages, the vendor dir approach seems to be a better fit.

[therecipe]

Will close this, since the status is tracked here #755 (comment) now